Abrasive, abrasive set, and method for polishing substrate

ABSTRACT

A polishing agent comprises: a fluid medium; an abrasive grain containing a hydroxide of a tetravalent metal element; a first additive; a second additive; and a third additive, wherein: the first additive is at least one selected from the group consisting of a compound having a polyoxyalkylene chain and a vinyl alcohol polymer; the second additive is a cationic polymer; and the third additive is an amino group-containing sulfonic acid compound.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 15/108,001, filed inthe U.S. on Jun. 24, 2016, which is a national phase application filedunder 35 U.S.C. 371 of International Application PCT/JP2014/073980,filed on Sep. 10, 2014, which claims priority from Japanese PatentApplication No. JP 2013-268956, filed Dec. 26, 2013, the entire contentof each of which is hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a polishing agent, a polishing agentset, and a method for polishing a base. In particular, the inventionrelates to a polishing agent, a polishing agent set, and a method forpolishing a base, used in manufacturing steps of semiconductor elements.

BACKGROUND ART

As manufacturing techniques of ULSI semiconductor elements, processingtechniques for densification and miniaturization of the semiconductorelements have been presently researched and developed. CMP (ChemicalMechanical Polishing) technique is one of the processing techniques likethis. A flattening technique using CMP has become an essential techniquefor flattening interlayer insulating materials, forming STI (ShallowTrench Isolation), forming plugs, forming embedded metal wires(damascene step), or the like, in manufacturing steps of semiconductorelements. A CMP step (flattening step using a CMP technique) isgenerally performed by supplying a CMP polishing agent between apolishing pad (polishing cloth) and a material to be polished of a baseand by polishing the material to be polished with the polishing pad.

Various polishing agents have been known as the CMP polishing agent usedfor CMP. When the CMP polishing agent is classified according to thekinds of abrasive grains (polishing particles), there have been known aceria-based polishing agent comprising cerium oxide (ceria) particles, asilica-based polishing agent comprising silicon oxide (silica)particles, an alumina-based polishing agent comprising aluminum oxide(alumina) particles, a resin particle-based polishing agent comprisingorganic resin particles, or the like.

Incidentally, in recent years, achievement of further miniaturization ofwires has been required in manufacturing steps of semiconductorelements, and polishing scratches generated during polishing have becomea problem. More specifically, when polishing is performed usingconventional polishing agents, generation of fine polishing scratchesgives no problem as long as the size of the polishing scratches issmaller than the conventional wire width, but becomes a problem in thecase where further miniaturization of wires is tried to be achieved.

For this problem, the average particle diameter of the abrasive grainscomprised in the polishing agent is tried to be reduced. However, if theaverage particle diameter is reduced, the polishing rate is decreaseddue to a decrease in the mechanical action. It is extremely difficult toachieve both a polishing rate and polishing scratches in this manner. Inresponse to this, polishing agents using abrasive grains including ahydroxide of a tetravalent metal element have been studied (for example,refer to the following Patent Literatures 1 to 4).

In CMP steps or the like for formation of STIs, polishing is performedfor a laminated product including a substrate having an irregularitypattern, a stopper (polishing stop layer) disposed on the convex part ofthe substrate, and an insulating material (for example, silicon oxide)disposed on the substrate and the stopper so as to fill the concave partof the substrate. The polishing of the insulating material is stopped bythe stopper during such a polishing. More specifically, the polishing ofthe insulating material is stopped at the stage where the stopper isexposed. This is because it is difficult to artificially control thepolished amount of the insulating material (for example, the removedfilm thickness in the insulating film), and the polishing degree iscontrolled by polishing the insulating material until the stopper isexposed. In this case, it is necessary to increase polishing selectivityfor insulating material with respect to stopper material (polishing rateratio: polishing rate for insulating material/polishing rate for stoppermaterial).

In response to the demand, a polishing agent comprising an additive hasbeen known (for example, refer to the following Patent Literature 5).According to this technique, there is described polishing of siliconoxide using silicon nitride as a stopper material by a polishing agentcomprising particles of a hydroxide of a tetravalent metal element andat least one of a cationic polymer and polysaccharide.

Silicon nitride is conventionally used as a stopper material, butpolysilicon is increasingly used as the stopper material in recentyears. In this case, it is necessary to further increase polishingselectivity for insulating material with respect to polysilicon. Inresponse to the demand, a polishing agent comprising an additive hasbeen known (for example, refer to the following Patent Literature 6).

CITATION LIST Patent Literature

-   Patent Literature 1: International Publication No. WO2002/067309-   Patent Literature 2: International Publication No. WO2012/070541-   Patent Literature 3: International Publication No. WO2012/070542-   Patent Literature 4: International Publication No. WO2012/070544-   Patent Literature 5: International Publication No. WO2009/131133-   Patent Literature 6: International Publication No. WO2013/125446

Non Patent Literature

-   Non Patent Literature 1: Complete Works of Dispersion Technology,    Johokiko Co., Ltd., July, 2005, Chapter 3, “Dispersers: Recent    development trends and selection criteria”

SUMMARY OF INVENTION Technical Problem

Incidentally, in CMP steps or the like for formation of STIs, afterpolishing insulating materials such as silicon oxide and stopping thepolishing at the stage where the stopper has been exposed, there is acase where extra polishing is performed even after exposure of thestopper in order to avoid residue of the insulating material on thestopper. Such extra polishing is referred to as “overpolishing”.

When overpolishing is performed simply using a polishing agent with highpolishing selectivity for insulating material with respect to stoppermaterial, the insulating material other than the insulating materiallocated on the stopper is also excessively polished. This promotesdishing (a phenomenon in which depressions (step heights) are producedin the insulating material serving as a device isolation layer) or thelike, and can result in inferior flatness after polishing. In CMP stepsor the like for formation of STIs, therefore, it is often necessary notonly to increase the polishing selectivity for insulating material withrespect to stopper material, but also to suppress excess polishing ofthe insulating material other than the insulating material located onthe stopper, when the stopper has been exposed.

It is an object of the present invention to solve these problems, andprovide a polishing agent, a polishing agent set, and a method forpolishing a base, which can obtain excellent polishing selectivity forinsulating material with respect to stopper material, and can achieve ahigh degree of flattening of the surface of a base after polishing, in aCMP technique for polishing an insulating material using a stopper.

Solution to Problem

A polishing agent of the present invention comprises: a fluid medium; anabrasive grain containing a hydroxide of a tetravalent metal element; afirst additive; a second additive; and a third additive, wherein: thefirst additive is at least one selected from the group consisting of acompound having a polyoxyalkylene chain and a vinyl alcohol polymer; thesecond additive is a cationic polymer; and the third additive is anamino group-containing sulfonic acid compound.

According to the polishing agent of the present invention, it ispossible to suppress excessive increase in the polishing rate forstopper material and improve the polishing rate for insulating material,compared to a conventional polishing agent, to obtain excellentpolishing selectivity for insulating material with respect to stoppermaterial. According to the polishing agent of the present invention,compared to a conventional polishing agent, it is also possible toreduce dishing after polishing to achieve a high degree of flattening ofthe surface of a base after polishing. Furthermore, according to thepolishing agent of the present invention, it is possible to polish theinsulating material with few polishing scratches, while achieving a highdegree of flattening of the surface of the base after polishing.

The second additive is preferably at least one selected from the groupconsisting of an allylamine polymer, a diallylamine polymer, avinylamine polymer and an ethyleneimine polymer. Thereby, it is possibleto obtain more excellent polishing selectivity for insulating materialwith respect to stopper material.

The third additive may be at least one selected from the groupconsisting of sulfamic acid, an aliphatic aminosulfonic acid, anaromatic aminosulfonic acid and their salts. Thereby, it is possible tofurther improve flatness.

A content of the third additive is preferably 0.0005 mass % or more and0.2 mass % or less based on a total mass of the polishing agent.Thereby, it is possible to further improve the polishing rate forinsulating material and to further improve flatness.

The hydroxide of a tetravalent metal element preferably contains ananion (excluding a hydroxide ion) bonded to the tetravalent metalelement. Thereby, it is possible to further improve the polishing ratefor insulating material.

One aspect of the present invention relates to use of the polishingagent for polishing of a surface to be polished containing siliconoxide. More specifically, the polishing agent of the present inventionis preferably used for polishing of a surface to be polished containingsilicon oxide.

A polishing agent set of the present invention comprises constituentcomponents of the polishing agent stored as separate liquids containinga first liquid and a second liquid, wherein the first liquid containsthe abrasive grain, and the second liquid contains at least one selectedfrom the group consisting of the first additive, the second additive andthe third additive. According to the polishing agent set of the presentinvention, it is possible to obtain the same effect as that of thepolishing agent of the present invention.

A first aspect of a method for polishing a base of the present inventioncomprises a step of polishing a surface to be polished of a base usingthe polishing agent. According to this method for polishing a base, itis possible to obtain the same effect as that of the polishing agent ofthe present invention by using the polishing agent.

A second aspect of a method for polishing a base of the presentinvention comprises a step of polishing a surface to be polished of abase using a polishing agent obtained by mixing at least the firstliquid and the second liquid of the polishing agent set. According tothis method for polishing a base, it is possible to obtain the sameeffect as that of the polishing agent of the present invention by usingthe polishing agent set.

A third aspect of a method for polishing a base of the present inventionis a method for polishing a base having an insulating material and astopper material, and comprises a step of selectively polishing theinsulating material with respect to the stopper material using thepolishing agent. According to this method for polishing a base, it ispossible to obtain the same effect as that of the polishing agent of thepresent invention by using the polishing agent.

A fourth aspect of a method for polishing a base of the presentinvention is a method for polishing a base having an insulating materialand a stopper material, and comprises a step of selectively polishingthe insulating material with respect to the stopper material using apolishing agent obtained by mixing the first liquid and the secondliquid of the polishing agent set. According to this method forpolishing a base, it is possible to obtain the same effect as that ofthe polishing agent of the present invention by using the polishingagent set.

In the method for polishing a base of the present invention, the stoppermaterial is preferably polysilicon. According to the method forpolishing a base of the present invention, it is possible to obtain thesame effect as that of the polishing agent of the present invention evenif polysilicon is used as the stopper material.

Advantageous Effects of Invention

According to the present invention, in a CMP technique for polishing aninsulating material (STI insulating material, pre-metal insulatingmaterial, interlayer insulating material or the like) using a stopper,it is possible to obtain excellent polishing selectivity for insulatingmaterial with respect to stopper material, and to achieve a high degreeof flattening of the surface of a base after polishing. According to thepresent invention, it is also possible to polish the insulating materialwith few polishing scratches, while achieving a high degree offlattening of the surface of the base after polishing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of anangle rotor.

FIG. 2 is a schematic cross-sectional view showing a pattern wafer usedin Examples.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a polishing agent, a polishing agent set, and a method forpolishing a base using the polishing agent or the polishing agent set,which are embodiments of the present invention, will be described indetail.

<Polishing Agent and Polishing Agent Set>

A polishing agent of the present embodiment is a composition whichcontacts a surface to be polished during polishing, and it is a CMPpolishing agent, for example. Specifically, the polishing agent of thepresent embodiment comprises: a fluid medium; an abrasive graincontaining a hydroxide of a tetravalent metal element; a first additive;a second additive; and a third additive, wherein: the first additive isat least one selected from the group consisting of a compound having apolyoxyalkylene chain and a vinyl alcohol polymer; the second additiveis a cationic polymer; and the third additive is an aminogroup-containing sulfonic acid compound. Hereinafter, essentialcomponents and optionally added components or the like will bedescribed.

(Abrasive Grains)

The polishing agent of the present embodiment comprises abrasive grainsincluding a hydroxide of a tetravalent metal element. The term“hydroxide of a tetravalent metal element” refers to a compoundcontaining a tetravalent metal ion (M⁴⁺) and at least one hydroxide ion(OH⁻). The hydroxide of a tetravalent metal element may contain an anionother than a hydroxide ion (for example, a nitrate ion NO₃ ⁻ and asulfate ion SO₄ ²⁻). For example, the hydroxide of a tetravalent metalelement preferably contains an anion (excluding a hydroxide ion, forexample, a nitrate ion NO₃ ⁻ and a sulfate ion SO₄ ²⁻) bonded to atetravalent metal element, and more preferably contains a nitrate ionNO₃ ⁻ bonded to the tetravalent metal element.

The hydroxide of a tetravalent metal element is preferably at least oneselected from the group consisting of a hydroxide of a rare earthelement and a hydroxide of zirconium from the viewpoint of suppressinggeneration of polishing scratches on a surface to be polished whilefurther improving polishing selectivity for an insulating material withrespect to a stopper material. From the viewpoint of further improvingthe polishing rate for insulating material, the tetravalent metalelement is preferably rare earth elements. Examples of rare earthelements which can be tetravalent include lanthanoids such as cerium,praseodymium and terbium, and from the viewpoint of easy availabilityand further excelling in a polishing rate, cerium is further preferable.A hydroxide of a rare earth element and a hydroxide of zirconium may beused together, or two or more kinds may be selected from rare earthelements.

The polishing agent of the present embodiment may further comprise otherkinds of abrasive grains within a range not impairing properties of theabrasive grains including the hydroxide of a tetravalent metal element.Specific examples thereof include abrasive grains including silica,alumina, zirconia, an organic resin or the like.

The lower limit of the content of the hydroxide of a tetravalent metalelement in the abrasive grains is preferably 50 mass % or more, morepreferably 60 mass % or more, further preferably 70 mass % or more,particularly preferably 80 mass % or more, and extremely preferably 90mass % or more, based on the total mass of the abrasive grains. It ispreferable that the abrasive grains are made of the hydroxide of atetravalent metal element (substantial 100 mass % of the abrasive grainsis particles of the hydroxide of a tetravalent metal element) from theviewpoint of easy preparation of the polishing agent and furtherexcelling in polishing properties, and it is more preferable that theabrasive grains are made of the hydroxide of tetravalent cerium(substantial 100 mass % of the abrasive grains is particles of thehydroxide of tetravalent cerium) from the viewpoint of high chemicalactivity and further excelling in a polishing rate.

In the constituent components of the polishing agent of the presentembodiment, the hydroxide of a tetravalent metal element is thought tohave a significant impact on polishing properties. Thus, by adjustingthe content of the hydroxide of a tetravalent metal element, a chemicalinteraction between the abrasive grains and a surface to be polished isimproved, and the polishing rate can be further improved. Morespecifically, the lower limit of the content of the hydroxide of atetravalent metal element is preferably 0.005 mass % or more, morepreferably 0.01 mass % or more, further preferably 0.03 mass % or more,and particularly preferably 0.05 mass % or more, based on the total massof the polishing agent, from the viewpoint of making it easier tosufficiently exhibit the function of the hydroxide of a tetravalentmetal element. The upper limit of the content of the hydroxide of atetravalent metal element is preferably 20 mass % or less, morepreferably 10 mass % or less, further preferably 5 mass % or less,particularly preferably 3 mass % or less, extremely preferably 1 mass %or less, very preferably 0.5 mass % or less, and still furtherpreferably 0.3 mass % or less, based on the total mass of the polishingagent, from the viewpoint of making it easier to avoid aggregation ofthe abrasive grains, and from the viewpoint of obtaining a favorablechemical interaction with the surface to be polished, and effectivelyusing properties of the abrasive grains.

In the polishing agent of the present embodiment, from the viewpoint ofmaking it easier to obtain a desired polishing rate, the lower limit ofthe content of the abrasive grains is preferably 0.005 mass % or more,more preferably 0.01 mass % or more, further preferably 0.02 mass % ormore, particularly preferably 0.03 mass % or more, and extremelypreferably 0.04 mass % or more, based on the total mass of the polishingagent. The upper limit of the content of the abrasive grains is notparticularly limited, but from the viewpoint of making it easier toavoid aggregation of the abrasive grains and allowing the abrasivegrains to effectively act on the surface to be polished to smoothlypromote polishing, it is preferably 20 mass % or less, more preferably10 mass % or less, further preferably 5 mass % or less, particularlypreferably 3 mass % or less, extremely preferably 1 mass % or less, verypreferably 0.5 mass % or less, and still further preferably 0.3 mass %or less, based on the total mass of the polishing agent.

In the case where the average particle diameter (average secondaryparticle diameter) of the abrasive grains is to some extent small, thespecific surface area of the abrasive grains which contact the surfaceto be polished is increased, and thus, the polishing rate can be furtherimproved, and the mechanical action is suppressed, and thus, polishingscratches can be further reduced. Therefore, the upper limit of theaverage particle diameter is preferably 300 nm or less, more preferably200 nm or less, further preferably 150 nm or less, particularlypreferably 100 nm or less, extremely preferably 80 nm or less, verypreferably 60 nm or less, and still further preferably 40 nm or less,from the viewpoint of obtaining a further excellent polishing rate forinsulating material and further reducing polishing scratches. The lowerlimit of the average particle diameter is preferably 1 nm or more, morepreferably 2 nm or more, and further preferably 3 nm or more, from theviewpoint of obtaining a further excellent polishing rate for insulatingmaterial and further reducing polishing scratches.

The average particle diameter of the abrasive grains can be measured bythe photon correlation method. Specifically, the average particlediameter can be measured using, for example, device name: Zetasizer3000HS manufactured by Malvern Instruments Ltd., device name: N5manufactured by Beckman Coulter, Inc. or the like. A measuring methodusing N5 can be performed as follows. Specifically, for example, anaqueous dispersion having a content of the abrasive grains adjusted to0.2 mass % is prepared, approximately 1 mL (L represents “liter”, thesame shall apply hereafter) of this aqueous dispersion is poured into a1-cm square cell, and the cell is placed in the device. A valueobtainable by performing measurement at 25° C. with a refractive indexand a viscosity of a dispersion medium set to 1.333 and 0.887 mPa·s canbe used as the average particle diameter of the abrasive grains.

[Content of Non-Volatile Component]

The abrasive grains are thought to comprise large particles withparticle sizes which can be measured with a particle size distributionmeter, and fine particles with particle sizes which cannot be measuredwith a particle size distribution meter. When an aqueous dispersioncomprising such abrasive grains dispersed in water has been centrifugedby the action of sufficient centrifugal force, the aqueous dispersion isthought to undergo solid-liquid separation mainly into a solid phase(precipitate) and a liquid phase (supernatant liquid), with the largeparticles settling as the solid phase and the fine particles floating upinto the liquid phase.

The present inventors have found that materials to be polished can bepolished at more excellent polishing rates by using abrasive grainswhich can produce a liquid phase with a high content of non-volatilecomponent when an aqueous dispersion comprising a sufficient amount ofthe abrasive grains has been centrifuged under specific conditions(conditions which allow action of centrifugal force which can adequatelyseparate the large particles and fine particles). More specifically, theabrasive grains of the present embodiment preferably produce a liquidphase with a content of non-volatile component of 500 ppm or more whenan aqueous dispersion having a content of the abrasive grains adjustedto 1.0 mass % has been centrifuged for 50 min (“min” represents“minute”) at a centrifugal acceleration of 1.59×10⁵ G.

The present inventors conjecture the following as the reason for whichan improving effect on polishing rate is obtained when the content ofnon-volatile component contained in the centrifuged liquid phase ishigh. In the case where the slurry and polishing agent comprising theabrasive grains are centrifuged for 50 min at a centrifugal accelerationof 1.59×10⁵ G, substantially all abrasive grains generally settle.However, since the particle diameter is sufficiently small in thepresent embodiment, many fine particles which do not settle arecontained even if centrifuge separation is performed under theconditions above. More specifically, it is thought that an increasedcontent of non-volatile component increases the proportion of fineparticles in the abrasive grains, and enlarges the surface area of theabrasive grains contacting the surface to be polished. It is thoughtthat this promotes polishing by chemical action, and improves thepolishing rate.

From the viewpoint of obtaining a further excellent polishing rate, thelower limit of the content of non-volatile component of the liquid phaseis preferably 500 ppm or more, more preferably 700 ppm or more, andfurther preferably 800 ppm or more. The upper limit of the content ofnon-volatile component of the liquid phase is the total amount of thecontent of the abrasive grains, for example, 10000 ppm.

The apparatus used for the centrifugal separation may be an angle rotorhaving a tube positioned at a prescribed angle, and a swing rotor havinga variable tube angle, with the tube positioned horizontally or nearlyhorizontally during the centrifugal separation.

FIG. 1 is a schematic cross-sectional view showing an example of anangle rotor. The angle rotor AR has bilateral symmetry around a rotationaxis A1 as the center, and only one side (the left side of the figure)is shown in FIG. 1 while the other side (the right side of the figure)is omitted. In FIG. 1, A2 is the tube angle, R_(min) is the minimumradius from the rotation axis A1 to the tube, and R_(max) is the maximumradius from the rotation axis A1 to the tube. R_(av) is the averageradius from the rotation axis A1 to the tube, and is calculated as“(R_(min)+R_(max))/2”.

For this type of centrifugal separation apparatus, the centrifugalacceleration [units: G] can be calculated by the following formula.Centrifugal acceleration[G]=1118×R×N ²×10⁻⁸  (1)[In the formula, R represents the radius of rotation (cm), and Nrepresents the rotational speed per 1 min (rpm=min⁻¹).]

In the present embodiment, centrifugal separation is performed with therotational speed N set for a centrifugal acceleration of 1.59×10⁵ Gusing the value of the average radius R_(a), in FIG. 1 as the radius ofrotation R in formula (1). When a swing rotor is used instead of anangle rotor shown in FIG. 1, the minimum radius R_(min), maximum radiusR_(max) and average radius R_(av) are each calculated from the state ofthe tube in the centrifugal separation, to set the conditions.

For example, the abrasive grains may be separated into large particlesand fine particles using an ultracentrifuge 70P-72 manufactured byHitachi Koki Co., Ltd. as the angle rotor. Specifically, centrifugalseparation of the aqueous dispersion can be performed using 70P-72 inthe following manner, for example. First, an aqueous dispersion having acontent of the abrasive grains adjusted to 1.0 mass % is prepared, andafter filling a centrifuge tube (tube) with this, the centrifuge tube isplaced in a rotor. After rotating for 50 min at a rotational speed of50000 min⁻¹, the centrifuge tube is removed from the rotor and theliquid phase in the centrifuge tube is collected. The content ofnon-volatile component of the liquid phase can be calculated bymeasuring the mass of the collected liquid phase and the mass of theresidue after drying the liquid phase.

[Light Transmittance]

The polishing agent of the present embodiment preferably has hightransparency for visible light (visually transparent or nearlytransparent). Specifically, the abrasive grains comprised in thepolishing agent of the present embodiment preferably produce lighttransmittance of 50%/cm or more for light having a wavelength of 500 nmin an aqueous dispersion having a content of the abrasive grainsadjusted to 1.0 mass %. This makes it possible to further suppress areduction in the polishing rate due to the addition of an additive, andthus, it makes it easier to obtain other properties while maintainingthe polishing rate. From the same viewpoint, the lower limit of thelight transmittance is more preferably 60%/cm or more, furtherpreferably 70%/cm or more, particularly preferably 80%/cm or more,extremely preferably 90%/cm or more, very preferably 95%/cm or more,still further preferably 98%/cm or more, and further preferably 99%/cmor more. The upper limit of the light transmittance is 100%/cm.

The reason why the reduction in the polishing rate can be suppressed byadjusting the light transmittance of the abrasive grains in this manneris not understood in detail, but the present inventors conjecture asfollows. The action of the abrasive grains including the hydroxide of atetravalent metal element (for example, cerium), as abrasive grains, isthought to more dominantly depend on the chemical action than on themechanical action. Therefore, the number of the abrasive grains isthought to contribute to the polishing rate more than the size of theabrasive grains.

In the case where the light transmittance is low in an aqueousdispersion having a content of the abrasive grains adjusted to 1.0 mass%, it is thought that, in the abrasive grains present in the aqueousdispersion, particles having a large particle diameter (hereinafter,referred to as “coarse particles”) exist in relatively large numbers.When an additive is added to a polishing agent comprising such abrasivegrains, other particles aggregate around the coarse particles as nuclei.It is thought that, as a result, the number of the abrasive grains whichact on a surface to be polished per unit area (effective abrasive grainnumber) is reduced and the specific surface area of the abrasive grainswhich contact the surface to be polished is reduced, and thus, thepolishing rate reduces.

On the other hand, in the case where the light transmittance is high inan aqueous dispersion having a content of the abrasive grains adjustedto 1.0 mass %, it is thought that the abrasive grains present in theaqueous dispersion are in a state where the above-described “coarseparticles” are small in number. In the case where the abundance of thecoarse particles is low in this manner, even when an additive is addedto a polishing agent, the coarse particles which are to be nuclei foraggregation are small in number. For this reason, aggregation betweenabrasive grains is suppressed or the size of aggregated particles isrelatively small. It is thought that, as a result, the number of theabrasive grains which act on a surface to be polished per unit area(effective abrasive grain number) is maintained and the specific surfacearea of the abrasive grains which contact the surface to be polished ismaintained, and thus, the reduction in the polishing rate becomesdifficult to occur.

According to the study by the present inventors, it was found that, evenamong polishing agents in which particle diameters of abrasive grainsmeasured by a common particle diameter measuring device are the same,some may be visually transparent (high light transmittance) and some maybe visually turbid (low light transmittance). Accordingly, it is thoughtthat the coarse particles which can produce the action described abovecontribute to the reduction in the polishing rate even by a very slightamount which cannot be detected by a common particle diameter measuringdevice.

The above-described light transmittance is transmittance for lighthaving a wavelength of 500 nm. The above-described light transmittanceis measured by a spectrophotometer, and specifically, is measured by aspectrophotometer U3310 (device name) manufactured by Hitachi, Ltd., forexample.

As a more specific measuring method, an aqueous dispersion having acontent of the abrasive grains adjusted to 1.0 mass % is prepared as ameasuring sample. Approximately 4 mL of this measuring sample is pouredinto a 1-cm square cell, and the cell is placed in the device andmeasurement is performed. In the case where the light transmittance is50%/cm or more in an aqueous dispersion having a content of the abrasivegrains of more than 1.0 mass %, it is clear that the light transmittanceis also 50%/cm or more in the case where it is diluted to 1.0 mass %.Therefore, the light transmittance can be screened by a simple method byusing an aqueous dispersion having a content of the abrasive grains ofmore than 1.0 mass %.

[Absorbance]

In the case where the abrasive grains including a hydroxide of atetravalent metal element produce absorbance of 1.00 or more for lighthaving a wavelength of 400 nm in an aqueous dispersion having a contentof the abrasive grains adjusted to 1.0 mass %, the polishing rate can befurther improved. The reason for this is not necessarily clear, but thepresent inventors conjecture as follows. More specifically, it isthought that, depending on manufacturing conditions of the hydroxide ofa tetravalent metal element or the like, particles having a compositionformula represented by M(OH)_(a)X_(b) (in the formula, a+b×c=4) composedof one tetravalent metal ion (M⁴⁺), 1 to 3 hydroxide ions (OH⁻) and 1 to3 anions (X^(c−)) are generated as a part of the abrasive grains (it isto be noted that the foregoing particles are also “the abrasive grainsincluding the hydroxide of a tetravalent metal element”). It is thoughtthat, in M(OH)_(a)X_(b), the electron-withdrawing anions (X^(c−)) act toimprove the reactivity of the hydroxide ions and the polishing rate isimproved as the abundance of M(OH)_(a)X_(b) is increased. It is thoughtthat, since the particles having a composition formula represented byM(OH)_(a)X_(b) absorb light having a wavelength of 400 nm, the polishingrate is improved as the abundance of M(OH)_(a)X_(b) is increased and theabsorbance for light having a wavelength of 400 nm is increased. Theabrasive grains including the hydroxide of a tetravalent metal elementmay be a dinuclear compound or a dinuclear complex as represented byM_(d)(OH)_(a)X_(b) (in the formula, a+b×c=4d), for example. Hereinafter,description will be made by using M(OH)_(a)X_(b) as an example.

It is thought that the abrasive grains including the hydroxide of atetravalent metal element may include not only particles having acomposition formula represented by M(OH)_(a)X_(b) but also particleshaving composition formulae represented by M(OH)₄, MO₂ or the like.Examples of the anions (X^(c−)) include NO₃ ⁻ and SO₄ ²⁻.

It is to be noted that the inclusion of the composition formulaM(OH)_(a)X_(b) in the abrasive grains can be confirmed, after washingthe abrasive grains with pure water well, by a method for detecting apeak corresponding to the anions (X^(c−)) using the FT-IR ATR method(Fourier transform InfraRed Spectrometer Attenuated Total ReflectionMethod). The existence of the anions (X^(c−)) can also be confirmed bythe XPS method (X-ray Photoelectron Spectroscopy). The existence ornon-existence of the bond of M and anions (X^(c−)) can also be confirmedby conducting EXAFS analysis from X-ray absorption fine structure (XAFS)measurement.

The absorption peak of M(OH)_(a)X_(b) (for example, M(OH)₃X) at awavelength of 400 nm has been confirmed to be much smaller than theabsorption peak at a wavelength of 290 nm described below. In thisregard, the present inventors studied the magnitude of absorbance usingan aqueous dispersion having an abrasive grain content of 1.0 mass %,which has a relatively high abrasive grain content and whose absorbanceis easily detected to a greater degree, and as a result, found that apolishing rate improving effect is excellent in the case of usingabrasive grains which produce absorbance of 1.00 or more for lighthaving a wavelength of 400 nm in such aqueous dispersion. Since theabsorbance for light having a wavelength of 400 nm is thought to bederived from the abrasive grains as described above, the above-describedpolishing rate improving effect cannot be obtained with a polishingagent comprising a substance which produces absorbance of 1.00 or morefor light having a wavelength of 400 nm (for example, a pigmentcomponent which exhibits a yellow color) in place of the abrasive grainswhich produce absorbance of 1.00 or more for light having a wavelengthof 400 nm.

The lower limit of the absorbance for light having a wavelength of 400nm is preferably 1.00 or more, more preferably 1.20 or more, furtherpreferably 1.40 or more, and particularly preferably 1.45 or more fromthe viewpoint of obtaining a further excellent polishing rate.

In the case where the abrasive grains including the hydroxide of atetravalent metal element produce absorbance of 1.000 or more for lighthaving a wavelength of 290 nm in an aqueous dispersion having a contentof the abrasive grains adjusted to 0.0065 mass %, the polishing rate canbe further improved. The reason for this is not necessarily clear, butthe present inventors conjecture as follows. More specifically,particles having a composition formula represented by M(OH)_(a)X_(b)(for example, M(OH)₃X), which are generated depending on manufacturingconditions of the hydroxide of a tetravalent metal element or the like,have a calculated absorption peak at a wavelength of about 290 nm, andfor example, particles composed of Ce⁴⁺(OH⁻)₃NO₃ ⁻ have an absorptionpeak at a wavelength of 290 nm. Thus, it is thought that, as theabundance of M(OH)_(a)X_(b) is increased and the absorbance for lighthaving a wavelength of 290 nm is increased, the polishing rate isimproved.

The absorbance for light having a wavelength of about 290 nm tends to bedetected to a greater degree as the measuring limit is exceeded. In thisregard, the present inventors studied the magnitude of absorbance usingan aqueous dispersion having an abrasive grain content of 0.0065 mass %,which has a relatively low abrasive grain content and whose absorbanceis easily detected to a small degree, and as a result, found that apolishing rate improving effect is excellent in the case of usingabrasive grains which produce absorbance of 1.000 or more for lighthaving a wavelength of 290 nm in such aqueous dispersion. Moreover, thepresent inventors found that, as absorbance of abrasive grains for lighthaving a wavelength of about 290 nm becomes high, yellowishness of apolishing agent and slurry using such abrasive grains becomes deep, andfound that the polishing rate is improved as the yellowishness of thepolishing agent and slurry becomes deep. The present inventors foundthat the absorbance for light having a wavelength of 290 nm in anaqueous dispersion having an abrasive grain content of 0.0065 mass % iscorrelated with the absorbance for light having a wavelength of 400 nmin an aqueous dispersion having an abrasive grain content of 1.0 mass %.

The lower limit of the absorbance for light having a wavelength of 290nm is preferably 1.000 or more, more preferably 1.050 or more, furtherpreferably 1.100 or more, particularly preferably 1.150 or more, andextremely preferably 1.200 or more, from the viewpoint of polishing amaterial to be polished at a further excellent polishing rate. The upperlimit of the absorbance for light having a wavelength of 290 nm is notparticularly limited, but it is preferably 10.000 or less, for example.

A material to be polished can be polished at a further excellentpolishing rate in the case where the abrasive grains which produceabsorbance of 1.00 or more for light having a wavelength of 400 nmproduce absorbance of 1.000 or more for light having a wavelength of 290nm in an aqueous dispersion having a content of the abrasive grainsadjusted to 0.0065 mass %.

The hydroxide of a tetravalent metal element (for example,M(OH)_(a)X_(b)) tends not to absorb light having a wavelength of 450 nmor more, particularly light having a wavelength of 450 to 600 nm.Therefore, from the viewpoint of suppressing adverse impacts onpolishing by inclusion of impurities and polishing a material to bepolished at a further excellent polishing rate, the abrasive grainspreferably produce absorbance of 0.010 or less for light having awavelength of 450 to 600 nm in an aqueous dispersion having a content ofthe abrasive grains adjusted to 0.0065 mass % (65 ppm). Morespecifically, absorbance for all of light within a range of a wavelengthof 450 to 600 nm preferably does not exceed 0.010 in the aqueousdispersion having a content of the abrasive grains adjusted to 0.0065mass %. The lower limit of the absorbance for light having a wavelengthof 450 to 600 nm is preferably 0.

The absorbance in an aqueous dispersion can be measured, for example,using a spectrophotometer (device name: U3310) manufactured by Hitachi,Ltd. Specifically, for example, an aqueous dispersion having a contentof the abrasive grains adjusted to 1.0 mass % or 0.0065 mass % isprepared as a measuring sample. Approximately 4 mL of the measuringsample is poured into a 1-cm square cell, and the cell is placed in thedevice. Next, absorbance measurement is performed within a range of awavelength of 200 to 600 nm, and the absorbance is determined from theobtained chart.

If absorbance of 1.00 or more is exhibited in the case where theabsorbance for light having a wavelength of 400 nm is measured byexcessively diluting such that the content of the abrasive grains isless than 1.0 mass %, the absorbance may be screened by assuming thatthe absorbance is 1.00 or more in the case where the content of theabrasive grains is 1.0 mass %. If absorbance of 1.000 or more isexhibited in the case where the absorbance for light having a wavelengthof 290 nm is measured by excessively diluting such that the content ofthe abrasive grains is less than 0.0065 mass %, the absorbance may bescreened by assuming that the absorbance is 1.000 or more in the casewhere the content of the abrasive grains is 0.0065 mass %. If absorbanceof 0.010 or less is exhibited in the case where the absorbance for lighthaving a wavelength of 450 to 600 nm is measured by diluting such thatthe content of the abrasive grains is more than 0.0065 mass %, theabsorbance may be screened by assuming that the absorbance is 0.010 orless in the case where the content of the abrasive grains is 0.0065 mass%.

The absorbance and light transmittance in which the abrasive grainsproduce in the aqueous dispersion can be measured by, after removingsolid components other than the abrasive grains and liquid componentsother than water, preparing an aqueous dispersion having a predeterminedabrasive grain content and using the aqueous dispersion. For removingthe solid components or the liquid components, although varyingdepending on components comprised in the polishing agent, centrifugationmethods such as centrifugation using a centrifuge capable of applyinggravitational acceleration of several thousand G or less, andultracentrifugation using an ultracentrifuge capable of applyinggravitational acceleration of several tens of thousands G or more;chromatography methods such as partition chromatography, adsorptionchromatography, gel permeation chromatography, and ion-exchangechromatography; filtration methods such as natural filtration,filtration under reduced pressure, pressure filtration, andultrafiltration; distillation methods such as distillation under reducedpressure, and atmospheric distillation; or the like, can be used, orthese may be combined as appropriate.

Examples of methods in the case where the polishing agent comprises acompound having a weight-average molecular weight of several tens ofthousands or more (for example, 50000 or more) include chromatographymethods and filtration methods, and gel permeation chromatography andultrafiltration are preferable. In the case of using filtration methods,the abrasive grains comprised in the polishing agent can be made to passthrough a filter by setting appropriate conditions. Examples of methodsin the case where the polishing agent comprises a compound having aweight-average molecular weight of several tens of thousands or less(for example, less than 50000) include chromatography methods,filtration methods, and distillation methods, and gel permeationchromatography, ultrafiltration, and distillation under reduced pressureare preferable. Examples of methods in the case where the polishingagent comprises abrasive grains other than the abrasive grains includingthe hydroxide of a tetravalent metal element include filtration methodsand centrifugation methods, and much abrasive grains including thehydroxide of a tetravalent metal element are comprised in a filtrate inthe case of filtration and in a liquid phase in the case ofcentrifugation.

As a method for separating the abrasive grains by the above-describedchromatography methods, for example, the abrasive grain can befractionated and/or other components can be fractionated by thefollowing conditions.

Sample solution: polishing agent 100 μL

Detector: UV-VIS Detector manufactured by Hitachi, Ltd., product name“L-4200”, wavelength: 400 nm

Integrator: GPC Integrator manufactured by Hitachi, Ltd., product name“D-2500”

Pump: manufactured by Hitachi, Ltd., product name “L-7100”

Column: packing column for water-based HPLC manufactured by HitachiChemical Co., Ltd., product name “GL-W550S”

Eluent: deionized water

Measuring temperature: 23° C.

Flow rate: 1 mL/min (pressure: about 40 to 50 kg/cm²)

Measurement time: 60 min

It is to be noted that deaeration treatment of an eluent is preferablyperformed using a deaerator before performing chromatography. In thecase where a deaerator cannot be used, an eluent is preferablydeaeration-treated in advance with ultrasonic wave or the like.

The abrasive grain may not be able to be fractionated under theabove-described conditions depending on components comprised in thepolishing agent, in this case, the abrasive grain can be separated byoptimizing the amount of a sample solution, the kind of a column, thekind of an eluent, a measuring temperature, a flow rate, or the like.Moreover, by adjusting the pH of the polishing agent, distillation timeof the components comprised in the polishing agent is adjusted, and itmay be separated from the abrasive grains. In the case where thepolishing agent comprises insoluble components, the insoluble componentsare preferably removed by filtration, centrifugation or the like, asnecessary.

[Preparation Method of Abrasive Grains]

The hydroxide of a tetravalent metal element can be prepared by causinga salt of a tetravalent metal element (metal salt) to react with analkali source (base). The hydroxide of a tetravalent metal element ispreferably prepared by mixing a salt of a tetravalent metal element withan alkali liquid (for example, alkali aqueous solution). This makes itpossible to obtain particles having an extremely fine particle diameter,and obtain a polishing agent which further excels in a reducing effecton polishing scratches. Such a method is disclosed in Patent Literature4, for example. The hydroxide of a tetravalent metal element can beobtained by mixing a metal salt solution comprising a salt of atetravalent metal element (for example, metal salt aqueous solution)with an alkali liquid. It is to be noted that, in the case where atleast one of the salt of a tetravalent metal element and the alkalisource is supplied to a reaction system in a liquid state, a means forstirring a mixed liquid is not limited. Examples thereof include amethod of stirring the mixed liquid using a rod-like, plate-like orpropeller-like stirrer, or stirring blade, which rotates around arotation axis; a method of stirring the mixed liquid by rotating astirrer using a magnetic stirrer which transmits power from the outsideof a container with a rotating magnetic field; a method of stirring themixed liquid with a pump placed on the outside of a tank; and a methodof stirring the mixed liquid by pressurizing outside air and furiouslyblowing it into a tank. As the salt of a tetravalent metal element,known one may be used without any particular restrictions, and examplesthereof include M(NO₃)₄, M(SO₄)₂, M(NH₄)₂(NO₃)₆, M(NH₄)₄(SO₄)₄ (where Mrepresents a rare earth metal element) and Zr(SO₄)₂.4H₂O, among these,M(NH₄)₂(NO₃)₆ is preferable. M is preferably cerium (Ce) which ischemically active. As described above, the salt of a tetravalent metalelement (metal salt) is more preferably ceric ammonium nitrate(Ce(NH₄)₂(NO₃)₆).

Examples of a means for adjusting the absorbance and the lighttransmittance include optimization of the manufacturing method of thehydroxide of a tetravalent metal element. Specific examples of a methodfor altering the absorbance for light having a wavelength of 400 nm andthe absorbance for light having a wavelength of 290 nm include selectionof the alkali source in the alkali liquid, adjustment of the rawmaterial concentrations in the metal salt solution and the alkaliliquid, adjustment of the mixing rate of the metal salt solution and thealkali liquid, and adjustment of the liquid temperature of the mixedliquid obtained by mixing the salt of a tetravalent metal element withthe alkali source. Specific examples of a method for altering the lighttransmittance for light having a wavelength of 500 nm include adjustmentof the raw material concentrations in the metal salt solution and thealkali liquid, adjustment of the mixing rate of the metal salt solutionand the alkali liquid, adjustment of the stirring rate when mixing, andadjustment of the liquid temperature of the mixed liquid.

In order to increase the absorbance for light having a wavelength of 400nm, the absorbance for light having a wavelength of 290 nm, and thelight transmittance for light having a wavelength of 500 nm, themanufacturing method of the hydroxide of a tetravalent metal element ispreferably more “moderate”. The term “moderate” means that an increasein pH is moderated (slowed) when the pH of the reaction system isincreased as the reaction proceeds. Conversely, in order to reduce theabsorbance for light having a wavelength of 400 nm, the absorbance forlight having a wavelength of 290 nm, and the light transmittance forlight having a wavelength of 500 nm, the manufacturing method of thehydroxide of a tetravalent metal element is preferably more “intensive”.The term “intensive” means that an increase in pH is intensified(quickened) when the pH of the reaction system is increased as thereaction proceeds. In order for the values of the absorbance and thelight transmittance to be in predetermined ranges, the manufacturingmethod of the hydroxide of a tetravalent metal element is preferablyoptimized by reference to the above-described tendency. Hereinafter, acontrolling method of the absorbance and the light transmittance will bedescribed in more detail.

{Alkali Source}

As the alkali source in the alkali liquid, known one can be used withoutany particular restrictions. Examples of the alkali source includeorganic bases and inorganic bases. Examples of the organic bases includenitrogen-containing organic bases such as guanidine, triethylamine, andchitosan; nitrogen-containing heterocyclic organic bases such aspyridine, piperidine, pyrrolidine, and imidazole; and ammonium saltssuch as ammonium carbonate, ammonium hydrogen carbonate,tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide,tetramethylammonium chloride, and tetraethylammonium chloride. Examplesof the inorganic bases include ammonia, and inorganic salts of alkalimetal, such as lithium hydroxide, sodium hydroxide, potassium hydroxide,calcium hydroxide, lithium carbonate, sodium carbonate, potassiumcarbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, andpotassium hydrogen carbonate. The alkali sources can be used singly orin combinations of two or more.

From the viewpoint of further improving the polishing rate forinsulating material, the alkali source is preferably ammonia andimidazole, and further preferably imidazole. In order to increase theabsorbance for light having a wavelength of 400 nm and the absorbancefor light having a wavelength of 290 nm, as the alkali source, an alkalisource which exhibits weak basicity is preferably used. Among the alkalisources, nitrogen-containing heterocyclic organic bases are preferable,pyridine, piperidine, pyrrolidine and imidazole are more preferable,pyridine and imidazole are further preferable, and imidazole isparticularly preferable.

{Concentration}

By controlling the raw material concentrations in the metal saltsolution and the alkali liquid, the absorbance for light having awavelength of 400 nm, the absorbance for light having a wavelength of290 nm, and the light transmittance for light having a wavelength of 500nm can be altered. Specifically, the absorbance tends to be increased byincreasing the metal salt concentration of the metal salt solution, andthe absorbance tends to be increased by decreasing the alkaliconcentration (concentration of base, concentration of alkali source) ofthe alkali liquid. The light transmittance tends to be increased byincreasing the metal salt concentration, and the light transmittancetends to be increased by decreasing the alkali concentration.

From the viewpoint of making it easier to achieve both an excellentpolishing rate and excellent stability of the abrasive grains, the upperlimit of the metal salt concentration in the metal salt solution ispreferably 1.000 mol/L or less, more preferably 0.500 mol/L or less,further preferably 0.300 mol/L or less, and particularly preferably0.200 mol/L or less, based on the total of the metal salt solution. Fromthe viewpoint of capable of suppressing rapid occurrence of a reaction(capable of moderating increase in pH) and increasing the absorbance forlight having a wavelength of 400 nm, the absorbance for light having awavelength of 290 nm, and the light transmittance for light having awavelength of 500 nm, the lower limit of the metal salt concentration ispreferably 0.010 mol/L or more, more preferably 0.020 mol/L or more, andfurther preferably 0.030 mol/L or more, based on the total of the metalsalt solution.

From the viewpoint of suppressing rapid occurrence of a reaction, theupper limit of the alkali concentration in the alkali liquid ispreferably 15.0 mol/L or less, more preferably 12.0 mol/L or less, andfurther preferably 10.0 mol/L or less, based on the total of the alkaliliquid. The lower limit of the alkali concentration is not particularlylimited, but from the viewpoint of productivity, it is preferably 0.001mol/L or more based on the total of the alkali liquid.

It is preferable that the alkali concentration in the alkali liquid isadjusted as appropriate depending on the alkali source selected. Forexample, in the case of an alkali source having pKa of conjugate acid ofthe alkali source of 20 or more, from the viewpoint of suppressing rapidoccurrence of a reaction, the upper limit of the alkali concentration ispreferably 0.10 mol/L or less, and more preferably 0.05 mol/L or less,based on the total of the alkali liquid. The lower limit of the alkaliconcentration is not particularly limited, but from the viewpoint ofsuppressing the amount used of a solution used for obtaining apredetermined amount of the hydroxide of a tetravalent metal element, itis preferably 0.001 mol/L or more based on the total of the alkaliliquid.

In the case of an alkali source having pKa of conjugate acid of thealkali source of 12 or more and less than 20, from the viewpoint ofsuppressing rapid occurrence of a reaction, the upper limit of thealkali concentration is preferably 1.0 mol/L or less, and morepreferably 0.50 mol/L or less, based on the total of the alkali liquid.The lower limit of the alkali concentration is not particularly limited,but from the viewpoint of suppressing the amount used of a solution usedfor obtaining a predetermined amount of the hydroxide of a tetravalentmetal element, it is preferably 0.01 mol/L or more based on the total ofthe alkali liquid.

In the case of an alkali source having pKa of conjugate acid of thealkali source of less than 12, from the viewpoint of suppressing rapidoccurrence of a reaction, the upper limit of the alkali concentration ispreferably 15.0 mol/L or less, and more preferably 10.0 mol/L or less,based on the total of the alkali liquid. The lower limit of the alkaliconcentration is not particularly limited, but from the viewpoint ofsuppressing the amount used of a solution used for obtaining apredetermined amount of the hydroxide of a tetravalent metal element, itis preferably 0.10 mol/L or more based on the total of the alkaliliquid.

Examples of the alkali source having pKa of conjugate acid of the alkalisource of 20 or more include 1,8-diazabicyclo[5.4.0]undec-7-ene (pKa:25). Examples of the alkali source having pKa of conjugate acid of thealkali source of 12 or more and less than 20 include potassium hydroxide(pKa: 16) and sodium hydroxide (pKa: 13). Examples of the alkali sourcehaving pKa of conjugate acid of the alkali source of less than 12include ammonia (pKa: 9) and imidazole (pKa: 7). The pKa value ofconjugate acid of the alkali source used is not particularly limited aslong as the alkali concentration is appropriately adjusted, but pKa ofconjugate acid of the alkali source is preferably less than 20, morepreferably less than 12, further preferably less than 10, andparticularly preferably less than 8.

{Mixing Rate}

By controlling the mixing rate of the metal salt solution and the alkaliliquid, the absorbance for light having a wavelength of 400 nm, theabsorbance for light having a wavelength of 290 nm, and the lighttransmittance for light having a wavelength of 500 nm can be altered.Each of the absorbance and light transmittance tend to be increased byadjusting such that an increase in pH is moderated (slowed). Morespecifically, the absorbance tends to be increased by slowing the mixingrate, and the absorbance tends to be decreased by quickening the mixingrate. The light transmittance tends to be increased by slowing themixing rate, and the light transmittance tends to be decreased byquickening the mixing rate.

From the viewpoint of further suppressing rapid progression of areaction and further suppressing bias of a reaction in a limited part,the upper limit of the mixing rate is preferably 5.00×10⁻³ m³/min (5L/min) or less, more preferably 1.00×10⁻³ m³/min (1 L/min) or less,further preferably 5.00×10⁻⁴ m³/min (500 mL/min) or less, particularlypreferably 1.00×10⁻⁴ m³/min (100 mL/min) or less, extremely preferably1.00×10⁻⁵ m³/min (10 mL/min) or less, and very preferably 5.00×10⁻⁶m³/min (5 mL/min) or less. The lower limit of the mixing rate is notparticularly limited, but from the viewpoint of productivity, it ispreferably 1.00×10⁻⁷ m³/min (0.1 mL/min) or more.

{Stirring Rate}

By controlling the stirring rate when mixing the metal salt solution andthe alkali liquid, the light transmittance for light having a wavelengthof 500 nm can be altered. Specifically, the light transmittance tends tobe increased by quickening the stirring rate, and the lighttransmittance tends to be decreased by slowing the stirring rate.

From the viewpoint of capable of further suppressing bias of a reactionin a limited part and excelling in mixing efficiency, the lower limit ofthe stirring rate is preferably 30 min⁻¹ or more, more preferably 50min⁻¹ or more, further preferably 80 min⁻¹ or more, particularlypreferably 100 min⁻¹ or more, and extremely preferably 120 min⁻¹ ormore. The upper limit of the stirring rate is not particularly limited,and furthermore, it needs to be adjusted as appropriate depending on thesize and the shape of the stirring blade, but from the viewpoint ofsuppressing splash of a liquid, it is preferably 1000 min⁻¹ or less.

{Liquid Temperature (Synthesis Temperature)}

By controlling the liquid temperature of the mixed liquid obtained bymixing the salt of a tetravalent metal element with the alkali source,the absorbance for light having a wavelength of 400 nm, the absorbancefor light having a wavelength of 290 nm, and the light transmittance forlight having a wavelength of 500 nm can be altered, and abrasive grainscapable of achieving a desired polishing rate and storage stability canbe obtained. Specifically, the absorbance tends to be increased bylowering the liquid temperature, and the absorbance tends to bedecreased by raising the liquid temperature. The light transmittancetends to be increased by lowering the liquid temperature, and the lighttransmittance tends to be decreased by raising the liquid temperature.

The liquid temperature is, for example, a temperature in the mixedliquid, which can be read with a thermometer placed in the mixed liquid,and is preferably 0 to 100° C. From the viewpoint of suppressing a rapidreaction, the upper limit of the liquid temperature is preferably 100°C. or less, more preferably 60° C. or less, further preferably 55° C. orless, particularly preferably 50° C. or less, and extremely preferably45° C. or less. From the viewpoint of making a reaction easily proceed,the lower limit of the liquid temperature is preferably 0° C. or more,more preferably 10° C. or more, further preferably 20° C. or more, andparticularly preferably 30° C. or more.

The hydroxide of a tetravalent metal element synthesized by the methodabove sometimes contains impurities (for example, metal impurities), butthe impurities can be removed by washing. Washing of the hydroxide of atetravalent metal element can be accomplished by a method for repeatedsolid-liquid separation by centrifugal separation or the like. Washingcan also be accomplished by ion removal using centrifugal separation,dialysis, ultrafiltration, an ion exchange resin or the like. Theabsorbance for light having a wavelength of 450 to 600 nm can beadjusted by removing impurities.

When the obtained abrasive grains are aggregated, they can be dispersedin a fluid medium by an appropriate method. The method for dispersingthe abrasive grains in a fluid medium (for example, water) may bemechanical dispersion treatment with a homogenizer, an ultrasonicdisperser, a wet ball mill or the like, in addition to dispersiontreatment with a stirrer. The dispersion method and particle diametercontrol method may be the methods described in Non-Patent Literature 1,for example. It is possible to increase the dispersibility of theabrasive grains by performing the washing treatment above to lower theelectric conductivity (for example, 500 mS/m or less) of the dispersioncontaining the abrasive grains. Thus, the washing treatment above may beapplied as dispersion treatment, or the washing treatment above anddispersion treatment may be combined.

(Additives)

The polishing agent of the present embodiment comprises an additive. Theterm “additive” refers to a substance which is added to the polishingagent in addition to a fluid medium and abrasive grains, in order toadjust the polishing properties such as polishing rate and polishingselectivity; the polishing agent properties such as abrasive graindispersibility and storage stability, or the like.

[First Additive: Compound Having Polyoxyalkylene Chain and Vinyl AlcoholPolymer]

The polishing agent of the present embodiment comprises at least oneselected from the group consisting of a compound having apolyoxyalkylene chain and a vinyl alcohol polymer (excluding a compoundcorresponding to the compound having a polyoxyalkylene chain), as afirst additive. Since the first additive has a plurality of oxygen atomsin the molecule, the first additive has a suppressing effect onexcessive increase in the polishing rate for stopper material. It isconjectured that covering of the stopper material by the first additivemoderates progression of polishing by the abrasive grains and suppressesexcessive increase in the polishing rate for stopper material.

The first additive is preferably a compound having a polyoxyalkylenechain from the viewpoint of further improving flatness. Specifically,the first additive is preferably at least one selected from the groupconsisting of polyalkylene glycol, a polyoxyalkylene derivative andpolyglycerin, and more preferably at least one selected from the groupconsisting of polyalkylene glycol and a polyoxyalkylene derivative.

Examples of polyalkylene glycol include polyethylene glycol,polypropylene glycol and polybutylene glycol, and from the viewpoint offurther improving flatness, at least one selected from the groupconsisting of polyethylene glycol and polypropylene glycol ispreferable, and polyethylene glycol is more preferable.

Examples of the polyoxyalkylene derivative include a compound obtainedby introducing a functional group and/or a substituent group intopolyalkylene glycol, and a compound obtained by adding polyalkyleneoxide to an organic compound. Examples of the functional group andsubstituent group include alkyl ether, alkylphenyl ether, phenyl ether,styrenated phenyl ether, alkylamine, fatty acid ester, glycol ester,polyglyceryl ether, diglyceryl ether, sugar ether and sugar ester.

Examples of the polyoxyalkylene derivative include polyoxyethylenestyrenated phenyl ether (for example, NOIGEN (registered trademark) EAseries manufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.);polyoxyethylene alkyl ether (for example, EMULGEN (registered trademark)series manufactured by Kao Corporation); polyoxyethylene alkyl phenylether (for example, EMULZIT (registered trademark) series manufacturedby Dai-Ichi Kogyo Seiyaku Co., Ltd.); polyoxyethylene sorbitan fattyacid ester (for example, SOLGEN (registered trademark) TW seriesmanufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd.); polyoxy ethylenefatty acid ester (for example, EMANON (registered trademark) seriesmanufactured by Kao Corporation); polyoxyethylene alkylamine (forexample, AMIRAZIN (registered trademark) D manufactured by Dai-IchiKogyo Seiyaku Co., Ltd.); polyoxypropylene sorbitol (for example, UNIOL(registered trademark) HS-1600D manufactured by NOF Corporation);polyoxyalkylene diglyceryl ethers such as polyoxy ethylene diglycerylether (for example, SC-E series manufactured by Sakamoto Yakuhin KogyoCo., Ltd.) and polyoxypropylene diglyceryl ether (for example, SY-DPseries manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.);polyoxyalkylene polyglyceryl ethers such as polyoxy ethylenepolyglyceryl ether and polyoxypropylene polyglyceryl ether; and acompound having added polyalkylene oxide (for example, SURFYNOL(registered trademark) 465 manufactured by Air Products Japan; TMPseries manufactured by Nippon Nyukazai Co., Ltd.).

Polyglycerin is a polyglycerin with a glycerin mean polymerizationdegree of 3 or more (polyglycerin which is a trimer or more). The lowerlimit of the mean polymerization degree of the polyglycerin is 3 ormore, preferably 4 or more, more preferably 5 or more and furtherpreferably 10 or more, from the viewpoint of increasing the polishingrate for insulating material. The upper limit of the mean polymerizationdegree of the polyglycerin is not particularly limited, but from theviewpoint of production, it is preferably 100 or less, more preferably50 or less, and further preferably 30 or less. From the aboveviewpoints, the mean polymerization degree of the polyglycerin is morepreferably 3 or more and 100 or less.

A “vinyl alcohol polymer” is ideally a polymer having the followingstructural formula.

[In the formula, n represents a positive integer.]

However, since vinyl alcohol generally tends not to exist alone asstable compounds, the vinyl alcohol polymer is obtained by polymerizinga vinyl carboxylate monomer such as vinyl acetate monomer to obtainpoly(vinyl carboxylate), followed by saponification (hydrolysis) forthis. Thus, a vinyl alcohol polymer obtained using vinyl acetate monomeras the starting material, for example, has —OCOCH₃ and hydrolyzed —OH asfunctional groups in the molecule, and the proportion of —OH is definedas the saponification degree. That is, a vinyl alcohol polymer whosesaponification degree is not 100% has a structure which is substantiallya copolymer of vinyl acetate and vinyl alcohol. The vinyl alcoholpolymer may also be one in which a vinyl carboxylate monomer such asvinyl acetate monomer and other vinyl group-containing monomer (forexample, ethylene, propylene, styrene or vinyl chloride) arecopolymerized, and all or some of the portions derived from the vinylcarboxylate monomer are then saponified. Specific examples of such vinylalcohol polymer include PVA-403 manufactured by Kuraray Co., Ltd. andJC-25 manufactured by Japan Vam & Poval Co., Ltd. Herein, all of theseare collectively defined as “vinyl alcohol polymers”.

The vinyl alcohol polymer may be a derivative of a homopolymer of vinylalcohol (that is, a polymer with a saponification degree of 100%), andderivatives of copolymers of vinyl alcohol monomer and other vinylgroup-containing monomers (for example, ethylene, propylene, styrene,vinyl chloride and vinyl acetate). Examples of the aforementionedderivatives include compounds having at least a portion of the hydroxylgroups substituted with amino, carboxyl, ester groups or the like, andcompounds having at least a portion of the hydroxyl groups modified, andspecific examples thereof include reactive vinyl alcohol polymers (forexample, GOHSEFIMER (registered trademark) Z manufactured by NipponSynthetic Chemical Industry Co., Ltd.), cationized vinyl alcoholpolymers (for example, GOHSEFIMER (registered trademark) K manufacturedby Nippon Synthetic Chemical Industry Co., Ltd.), anionized vinylalcohol polymers (for example, GOHSERAN (registered trademark) L andGOHSENOL (registered trademark) T manufactured by Nippon SyntheticChemical Industry Co., Ltd.), and hydrophilic group-modified vinylalcohol polymers (for example, ECOMATI manufactured by Nippon SyntheticChemical Industry Co., Ltd.).

The upper limit of the saponification degree of the vinyl alcoholpolymer is preferably 90 mol % or less, more preferably 85 mol % orless, and further preferably 80 mol % or less, from the viewpoint ofobtaining more excellent polishing selectivity for insulating materialwith respect to stopper material. The lower limit of the saponificationdegree is not particularly limited, but from the viewpoint of excellentsolubility in water, it is preferably 50 mol % or more, more preferably60 mol % or more, and further preferably 70 mol % or more. Thesaponification degree of the vinyl alcohol polymer can be measuredaccording to JIS K 6726 (polyvinyl alcohol test method).

The upper limit of the mean polymerization degree of the vinyl alcoholpolymer is not particularly limited, but from the viewpoint of furtherimproving the polishing rate for insulating material, it is preferably3000 or less, more preferably 2000 or less, and further preferably 1000or less. From the viewpoint of obtaining a more excellent polishingselective ratio for insulating material with respect to stoppermaterial, the lower limit of the mean polymerization degree ispreferably 50 or more, more preferably 100 or more, and furtherpreferably 150 or more. The mean polymerization degree of the vinylalcohol polymer can be measured according to JIS K 6726 (polyvinylalcohol test method).

The first additive can be used as a single type alone or as acombination of two or more types, for the purpose of adjusting polishingproperties such as polishing selectivity and flatness.

From the viewpoint of further improving the polishing rate forinsulating material (for example, silicon oxide), the upper limit of theweight-average molecular weight of the first additive is preferably100×10³ or less, more preferably 80×10³ or less, further preferably50×10³ or less, particularly preferably 40×10³ or less, and extremelypreferably 30×10³ or less. From the viewpoint of further improving thepolishing selectivity and flatness, the lower limit of theweight-average molecular weight of the first additive is preferably 250or more, more preferably 400 or more, and further preferably 500 ormore. When the first additive is polyglycerin, the upper limit of theweight-average molecular weight of the first additive is preferably 250or more, more preferably 400 or more, further preferably 500 or more,particularly preferably 700 or more, and extremely preferably 750 ormore, from the viewpoint of further improving the polishing rate forinsulating material.

The weight-average molecular weight can be measured by gel permeationchromatography (GPC) under the following conditions, using a calibrationcurve of standard polystyrene, for example.

Device: Hitachi Model L-6000 [manufactured by Hitachi, Ltd.]

Column: GL-R420 Gel pack (registered trademark)+GL-R430 Gel pack(registered trademark)+GL-R440 Gel pack (registered trademark) (total of3, trade name, Hitachi Chemical Co., Ltd.)

Eluent: Tetrahydrofuran

Measuring temperature: 40° C.

Flow rate: 1.75 mL/min

Detector: L-3300RI [manufactured by Hitachi, Ltd.]

From the viewpoint of further improving the polishing rate forinsulating material, the lower limit of the first additive content ispreferably 0.01 mass % or more, more preferably 0.04 mass % or more,further preferably 0.1 mass % or more, and particularly preferably 0.3mass % or more, based on the total mass of the polishing agent. From theviewpoint of suppressing excessive increase in the viscosity of thepolishing agent, the upper limit of the first additive content ispreferably 10 mass % or less, more preferably 5.0 mass % or less,further preferably 3.0 mass % or less, and particularly preferably 2.0mass % or less, based on the total mass of the polishing agent. Fromthese viewpoints, the first additive content is more preferably 0.01mass % or more and 10 mass % or less, based on the total mass of thepolishing agent. When a plurality of compounds are used as the firstadditive, the total content of each of the compounds preferablysatisfies the range specified above. The content of the first additiveis preferably adjusted as appropriate depending on the method forpreparing the insulating material (the type and the film-formingcondition), from the viewpoint of further improving the polishing ratefor insulating material, polishing selectivity for insulating materialwith respect to stopper material, and flatness.

[Second Additive: Cationic Polymer]

The polishing agent of the present embodiment comprises a cationicpolymer as a second additive in addition to the first additive. The“cationic polymer” is a polymer having a cationic group, or a groupwhich can be ionized to a cationic group, on the main chain or the sidechain. The first additive is not included in the “second additive”.

The second additive has a suppressing effect on the polishing rate forstopper material, by using in combination with the first additive. It isthought that, since the second additive adsorbs onto the insulatingmaterial more readily, the excess first additive which is not able to beadsorbed due to adsorption of the second additive is adsorbed morethickly onto the stopper material surface, thereby suppressing polishingof the stopper material. The second additive also has an improvingeffect on the polishing rate for insulating material. When the firstadditive excessively covers the insulating material, the polishing ratefor insulating material is thought to be lowered. However, when thesecond additive is used together, it is though that interaction betweenthe first additive and the second additive suppresses excessive coveringof the insulating material. Thus, the polishing agent of the presentembodiment can improve the polishing selectivity for insulating materialwith respect to stopper material.

The second additive also has an increasing effect on the polishing ratefor insulating material without impairing flatness. The first additivesuitably cover the insulating material due to the presence of the secondadditive. Thereby, it is thought that the polishing rate for concaveparts of the insulating material is suppressed while improving thepolishing rate for convex parts of the insulating material, allowinghigh flatness to be maintained.

The second additive is preferably at least one selected from the groupconsisting of an allylamine polymer, a diallylamine polymer, avinylamine polymer and an ethyleneimine polymer, from the viewpoint ofobtaining more excellent polishing selectivity for insulating materialwith respect to stopper material. These polymers can be obtained bypolymerizing at least one monomer component selected from the groupconsisting of an allylamine compound, a diallylamine compound, avinylamine compound, an ethyleneimine compound and their derivatives.The polymers may have a structural unit derived from a monomer componentother than an allylamine compound, a diallylamine compound, a vinylaminecompound, an ethyleneimine compound and their derivatives, and it mayhave a structural unit derived from acrylamide, dimethylacrylamide,diethylacrylamide, hydroxyethylacrylamide, acrylic acid, methylacrylate, methacrylic acid, maleic acid, sulfur dioxide or the like.

The second additive may be a homopolymer of an allylamine compound, adiallylamine compound, a vinylamine compound, an ethyleneimine compoundor their derivatives. It may be a copolymer having a structural unitderived from an allylamine compound, a diallylamine compound, avinylamine compound, an ethyleneimine compound or their derivatives. Thestructural unit in the copolymer may have any desired sequence. Forexample, it may have any desired forms including (a) the form of a blockcopolymer with the same structural units in continuity, (b) the than ofa random copolymer having a structural unit A and a structural unit Barranged in no particular order, (c) the form of an alternatingcopolymer having a structural unit A and a structural unit B in analternating arrangement, or the like.

The allylamine polymer is a polymer obtained by polymerizing anallylamine compound or its derivative, and examples thereof include apolymer having a structural unit represented by the following generalformula (I) or (II). Examples of the allylamine compound includeallylamine, methylallylalmine, dimethylallylalmine andtrimethylallylammonium salts. Examples of the derivative of theallylamine compound include alkoxycarbonylated allylamine,methylcarbonylated allylamine, aminocarbonylated allylamine and ureatedallylamine.

[In the formula, R each independently represents a hydrogen atom or amonovalent organic group, and X⁻ represents an anion.]

The diallylamine polymer is a polymer obtained by polymerizing adiallylamine compound or its derivative, and examples thereof include apolymer having a structural unit represented by the following generalformula (III) or (IV). Examples of the diallylamine compound includediallylamine, methyldiallylamine, tert-butyldiallylamine,N,N-diarylaniline, N,N-diarylbenzylamin, and(α-methylbenzyl)diarylamine. Examples of the derivative of thediallylamine compound include a diallyldimethylammonium salt, adiallylmethylethylammonium salt, acylated diallylamine,aminocarbonylated diallylamine, alkoxycarbonylated diallylamine,aminothiocarbonylated diallylamine and hydroxyalkylated diallylamine.Examples of the ammonium salt includes ammonium chloride.

[In the formula, R each independently represents a hydrogen atom or amonovalent organic group, and X⁻ represents an anion.]

The vinylamine polymer is a polymer obtained by polymerizing avinylamine compound or its derivative, and examples thereof include apolymer having a structural unit represented by the following generalformula (V). Examples of the vinylamine compound include vinylamine,methylvinylamine, N,N-dimethylvinylamine, vinylethylamine,N,N-diethylvinylamine, N-vinylaniline, vinylbenzylamine,tert-butylvinylamine and allylvinylamine. Examples of the derivative ofthe vinylamine compound include alkylated vinylamine, amidatedvinylamine, ethylene oxidated vinylamine, propylene oxidated vinylamine,alkoxylated vinylamine, carboxymethylated vinylamine, acylatedvinylamine and ureated vinylamine.

[In the formula, R each independently represents a hydrogen atom or amonovalent organic group.]

The ethyleneimine polymer is a polymer obtained by polymerizing anethyleneimine compound or its derivative, and examples thereof include apolymer having a structural unit represented by the following generalformula (VI). Examples of the ethyleneimine compound includeethyleneimine. Examples of the ethyleneimine derivative include anaminoethylated acrylic polymer, alkylated ethyleneimine, ureatedethyleneimine and propylene oxidated ethyleneimine.

[In the formula, R represents a hydrogen atom or a monovalent organicgroup.]

Examples of the monovalent organic group of R in the formulae (I) to(VI) include alkyl groups such as a methyl group and an ethyl group; andallyl groups. Examples of X⁻ in the formulae (II) and (IV) include achloride ion, an ethyl sulfate ion and a methyl sulfate ion.

The second additive used may be acrylic polymers such as cation-modifiedpolyacrylamide and cation-modified polydimethylacrylamide;polysaccharides such as chitosan, a chitosan derivative, cation-modifiedcellulose and cation-modified dextran; and a copolymer obtained bypolymerizing a monomer derived from a structural unit composing thesecompounds.

From the viewpoint of further suppressing progression of dishing andgeneration of polishing scratches at the surface to be polished whilefurther improving the polishing selectivity for insulating material withrespect to stopper material, the second additive is preferably anallylamine polymer, a diallylamine polymer and an ethyleneimine polymer.From the same viewpoint, the allylamine polymer is preferably ahomopolymer in which all of R are hydrogen atoms in the formula (I); theethyleneimine polymer is preferably a homopolymer in which R is hydrogenatom in the formula (VI); the diallylamine polymer is preferably ahomopolymer in which all of R are organic groups in the formula (IV), acopolymer of a monomer in which all of R are organic groups in theformula (IV) and acrylamide, and a copolymer of a monomer in which allof R are organic groups in the formula (IV) and acrylic acid. The secondadditive is preferably, for example, polyallylamine, polyethyleneimine,a diallyldimethylammonium chloride/acrylamide copolymer and adiallyldimethylammonium chloride/acrylic acid copolymer. The secondadditive is preferably polyallylamine, polyethyleneimine and adiallyldimethylammonium chloride/acrylamide copolymer, from theviewpoint of further improving the polishing selectivity for insulatingmaterial with respect to stopper material and from the viewpoint offurther improving the polishing rate for insulating material. The secondadditive used can be a single type or a combination of two or moretypes, for the purpose of adjusting the polishing properties such aspolishing selectivity and flatness.

The lower limit of the weight-average molecular weight of the secondadditive is preferably 100 or more, more preferably 300 or more, furtherpreferably 500 or more, and particularly preferably 1000 or more, fromthe viewpoint of further improving the polishing selectivity forinsulating material with respect to stopper material. The upper limit ofthe weight-average molecular weight of the second additive is preferably1000×10³ or less, more preferably 800×10³ or less, further preferably600×10³ or less, and particularly preferably 400×10³ or less, from theviewpoint of further improving the polishing selectivity for insulatingmaterial with respect to stopper material. From the viewpoints above,the weight-average molecular weight of the second additive is morepreferably 100 or more and 1000×10³ or less. The weight-averagemolecular weight of the second additive can be measured by the samemethod as for the weight-average molecular weight of the first additive.

From the viewpoint of further improving the polishing selectivity andflatness, the lower limit of the content of the second additive ispreferably 0.0001 mass % or more, more preferably 0.0003 mass % or more,further preferably 0.0005 mass % or more, and particularly preferably0.0007 mass % or more, based on the total mass of the polishing agent.From the viewpoint of more excellent polishing selectivity, the upperlimit of the content of the second additive is preferably 5 mass % orless, more preferably 3 mass % or less, further preferably 1 mass % orless, particularly preferably 0.5 mass % or less, extremely preferably0.1 mass % or less, very preferably 0.05 mass % or less, and stillfurther preferably 0.01 mass % or less, based on the total mass of thepolishing agent. From the viewpoints above, the content of the secondadditive is more preferably 0.0001 mass % or more and 5 mass % or lessbased on the total mass of the polishing agent. When a plurality ofcompounds are used as the second additive, the total content of each ofthe compounds preferably satisfies the range specified above. Thecontent of the second additive is preferably adjusted as appropriatedepending on the method for preparing the insulating material (the typeand the film-forming condition), from the viewpoint of further improvingthe polishing rate for insulating material, polishing selectivity forinsulating material with respect to stopper material, and flatness.

The lower limit of the ratio of the content of the second additive withrespect to the content of the first additive is preferably 0.0005 ormore, more preferably 0.001 or more, further preferably 0.0015 or more,and particularly preferably 0.002 or more, in terms of mass ratio, fromthe viewpoint of further improving the polishing selectivity andflatness. The upper limit of the ratio of the content of the secondadditive with respect to the content of the first additive is preferably0.03 or less, more preferably 0.025 or less, further preferably 0.02 orless, and particularly preferably 0.015 or less, in terms of mass ratio,from the viewpoint of more excellent polishing selectivity. From theviewpoints above, the ratio of the content is more preferably 0.0005 ormore and 0.03 or less.

[Third Additive: Amino Group-Containing Sulfonic Acid Compound]

The polishing agent of the present embodiment comprises an aminogroup-containing sulfonic acid compound as the third additive, inaddition to the first additive and the second additive. The term “aminogroup-containing sulfonic acid compound” is a compound having at leastone selected from the group consisting of a sulfonic group (sulfo group,—SO₃H) and a sulfonate group (—SO₃M: M is a metal atom), and an aminogroup (—NH₃) in the molecule. Examples of the metal atom M of thesulfonate group include alkali metals such as Na and K, and alkali earthmetals such as Mg and Ca. Use of the third additive suppresses polishingof the insulating material (for example, the insulating materialembedded in the concave parts) after exposure of the stopper, therebyallowing high flatness to be obtained. However the reason for this isnot necessarily clear, present inventors conjecture as follows. Morespecifically, when polishing is progressed and the stopper is exposed,the area of the insulating material exposed on the surface isconsiderably decreased rather than before the stopper is exposed. Atthis time, it is thought that, since the third additive thought to havea high adsorption force to the insulating material and a low adsorptionforce to the stopper concentrates in the insulating material, the amountof adsorption of the third additive to the insulating material isincreased.

The third additive used can be at least one selected from the groupconsisting of sulfamic acid (alias name: amidosulfonic acid), analiphatic aminosulfonic acid, an aromatic aminosulfonic acid and saltsthereof. Use of such compounds can further improve flatness.

The aliphatic aminosulfonic acid compound is defined as an aliphaticcompound having an amino group and a sulfonic group. Specific examplesof the aliphatic aminosulfonic acid compound includeaminomethanesulfonic acid, aminoethanesulfonic acid (for example,1-aminoethanesulfonic acid and 2-aminoethanesulfonic acid (alias name:taurine)) and aminopropanesulfonic acid (for example,1-aminopropane-2-sulfonic acid and 2-aminopropane-1-sulfonic acid). Thearomatic aminosulfonic acid is defined as an aromatic compound(preferably, an aromatic hydrocarbon) having an amino group and asulfonic group. Specific examples of the aromatic aminosulfonic acidinclude aminobenzenesulfonic acid (for example, orthanilic acid (aliasname: 2-aminobenzenesulfonic acid), metanilic acid (alias name:3-aminobenzenesulfonic acid) and sulfanilic acid (alias name:4-aminobenzenesulfonic acid)), diaminobenzensulfonic acid (for example,2,4-diaminobenzensulfonic acid and 3,4-diaminobenzensulfonic acid) andaminonaphthalenesulfonic acid.

From the viewpoint of obtaining higher flatness, the molecular weight ofthe third additive is preferably 500 or less, more preferably 300 orless, further preferably 250 or less, and particularly preferably 200 orless. The lower limit of the molecular weight is preferably 100 or more,for example.

From the viewpoint of further suppressing polishing of the insulatingmaterial after exposure of the stopper (for example, the insulatingmaterial embedded in the concave parts), thereby allowing higherflatness to be obtained, the third additive is preferably at least oneselected from the group consisting of aliphatic aminosulfonic acid andaromatic aminosulfonic acid, more preferably at least one selected fromthe group consisting of aminoethanesulfonic acid andaminobenzenesulfonic acid, and further preferably at least one selectedfrom the group consisting of aminoethanesulfonic acid, orthanilic acid,metanilic acid, 2,4-diaminobenzensulfonic acid and sulfanilic acid. Thethird additive may be used as a single type alone or as a combination oftwo or more types, for the purpose of adjusting polishing propertiessuch as polishing selectivity and flatness.

From the viewpoint of further improving the flatness, the lower limit ofthe content of the third additive is preferably 0.0005 mass % or more,more preferably 0.001 mass % or more, further preferably 0.002 mass % ormore, and particularly preferably 0.003 mass % or more, based on thetotal mass of the polishing agent. From the viewpoint of furtherexcelling in a polishing rate for insulating material, the upper limitof the content of the third additive is preferably 0.2 mass % or less,more preferably 0.1 mass % or more, further preferably 0.07 mass % orless, particularly preferably 0.05 mass % or less, extremely preferably0.03 mass % or less, and very preferably 0.02 mass % or less, based onthe total mass of the polishing agent. From the viewpoints above, thecontent of the third additive is more preferably 0.0005 mass % or moreand 0.2 mass % or less based on the total mass of the polishing agent.When a plurality of compounds are used as the third additive, the totalcontent of each of the compounds preferably satisfies the rangespecified above. The content of the third additive is preferablyadjusted as appropriate depending on the method for preparing theinsulating material (the type and the film-forming condition), from theviewpoint of further improving the polishing rate for insulatingmaterial, polishing selectivity for insulating material with respect tostopper material, and flatness.

[Fourth Additive]

The polishing agent of the present embodiment may further comprise afourth additive, in addition to the first additive, the second additiveand the third additive, for the purpose of adjusting the polishingproperties such as a polishing rate; and the polishing agent propertiessuch as abrasive grain dispersibility and storage stability; or thelike.

Examples of the fourth additive include carboxylic acid and amino acid.These may be used as a single type alone or as a combination of two ormore types. Among these, preferred are carboxylic acid and amino acid,from the viewpoint of excellent balance between abrasive graindispersibility and polishing properties.

The carboxylic acid has the effect of stabilizing the pH and furtherimproving the polishing rate for insulating material. Examples of thecarboxylic acid include formic acid, acetic acid, propionic acid,butyric acid, valeric acid, caproic acid and lactic acid.

The amino acid has the effect of improving the dispersibility of theabrasive grains including the hydroxide of a tetravalent metal element,and further improving the polishing rate for insulating material.Examples of the amino acid include arginine, lysine, aspartic acid,glutamic acid, asparagine, glutamine, histidine, proline, tyrosine,tryptophan, serine, threonine, glycine, α-alanine, β-alanine,methionine, cysteine, phenylalanine, leucine, valine and isoleucine. Theamino acid has a carboxyl group, but it is defined as one different fromthe carboxylic acid.

When the fourth additive is used, the content of the fourth additive ispreferably 0.01 mass % or more and 10 mass % or less, based on the totalmass of the polishing agent, from the viewpoint of obtaining an additioneffect of the fourth additive while suppressing sedimentation of theabrasive grains. When a plurality of compounds are used as the fourthadditive, the total content of each of the compounds preferablysatisfies the range specified above.

[Water-Soluble Polymer]

The polishing agent of the present embodiment may further comprise awater-soluble polymer, for the purpose of adjusting the polishingproperties such as flatness, in-plane uniformity, polishing selectivityfor silicon oxide with respect to silicon nitride (polishing rate forsilicon oxide/polishing rate for silicon nitride), and polishingselectivity for silicon oxide with respect to polysilicon (polishingrate for silicon oxide/polishing rate for polysilicon). The term“water-soluble polymer” is defined as a polymer whose solubility to 100g of water at 25° C. is at least 0.1 g. The first additive and thesecond additive are not included in the “water-soluble polymer”.

Specific examples of the water-soluble polymer include, but are notparticularly limited to, polysaccharides such as alginic acid, pecticacid, carboxymethyl cellulose, agar, curdlan and guar gum; andvinyl-based polymers such as polyvinylpyrrolidone and polyacrolein. Thewater-soluble polymer can be used as a single type alone or as acombination of two or more types.

When the water-soluble polymer is used, the lower limit of the contentof the water-soluble polymer is preferably 0.0001 mass % or more, morepreferably 0.001 mass % or more, and further preferably 0.01 mass % ormore, based on the total mass of the polishing agent, from the viewpointof obtaining an addition effect of the water-soluble polymer whilesuppressing sedimentation of the abrasive grains. The upper limit of thecontent of the water-soluble polymer is preferably 5 mass % or less,more preferably 1 mass % or less, and further preferably 0.5 mass % orless, based on the total mass of the polishing agent, from the viewpointof obtaining an addition effect of the water-soluble polymer whilesuppressing sedimentation of the abrasive grains. From the viewpointsabove, the content of the water-soluble polymer is more preferably0.0001 mass % or more and 5 mass % or less based on the total mass ofthe polishing agent. When a plurality of compounds are used as thewater-soluble polymer, the total content of each of the compoundspreferably satisfies the range specified above.

(Fluid Medium)

The fluid medium in the polishing agent of the present embodiment is notparticularly limited, but it is preferably water such as deionized wateror ultrapure water. An organic solvent having solubility in water of 10g/100 g (H₂O) or more and being in the form of a liquid at 20° C.(excluding the first, second and third additives) may be comprised inthe polishing agent. The content of the fluid medium may be theremainder of the polishing agent excluding the content of otherconstituent components, and it is not particularly limited.

(Properties of Polishing Agent)

The lower limit of the pH of the polishing agent of the presentembodiment is preferably 3.0 or more, more preferably 4.0 or more,further preferably 4.5 or more, particularly preferably 5.0 or more,extremely preferably 5.5 or more, and very preferably 6.0 or more, fromthe viewpoint of further improving the polishing rate for insulatingmaterial and further improving flatness. The upper limit of the pH ispreferably 10.0 or less, more preferably 9.0 or less, further preferably8.0 or less, particularly preferably 7.0 or less, and extremelypreferably 6.5 or less, from the viewpoint of further improving thepolishing rate for insulating material and preventing generation ofpolishing residue for insulating material. From the viewpoints above,the pH of the polishing agent is more preferably 3.0 or more and 10.0 orless. The pH is defined as pH at a liquid temperature of 25° C.

The pH of the polishing agent can be adjusted with an acid componentsuch as an inorganic acid or an organic acid; an alkaline component suchas ammonia, sodium hydroxide, tetramethylammonium hydroxide (TMAH) orimidazole; or the like. A buffering agent may also be added to stabilizethe pH. A buffering agent may also be added as a buffer solution (abuffering agent-containing solution). Examples of such buffer solutioninclude an acetate buffer solution and a phthalate buffer solution.

The pH of the polishing agent of the present embodiment can be measuredwith a pH meter (for example, a Model PHL-40 by DKK Corp.).Specifically, for example, after 2-point calibration of a pH meter usinga phthalate pH buffer solution (pH 4.01) and a neutral phosphate pHbuffer solution (pH 6.86) as standard buffer solutions, the pH meterelectrode is placed in the polishing agent, and then the value ismeasured after at least 2 min passes for stabilization. At this time,the liquid temperatures of the standard buffer solution and polishingagent are both 25° C.

The polishing agent of the present embodiment may be stored as aone-pack polishing agent comprising at least the abrasive grains, thefirst additive, the second additive, the third additive and a fluidmedium, or it may be stored as a multi-pack (for example, two-pack)polishing agent set comprising constituent components of the polishingagent divided into a slurry (first liquid) and an additive solution(second liquid) so that the slurry and the additive solution are mixedto form the polishing agent. The slurry contains at least the abrasivegrains, for example. The additive solution contains at least oneselected from the group consisting of the first additive, the secondadditive and the third additive, for example. Between the slurry and theadditive solution, the first additive, the second additive, the thirdadditive, the fourth additive, the water-soluble polymer and thebuffering agent are preferably contained in the additive solution. Theconstituent components of the polishing agent may be stored as apolishing agent set divided into three or more liquids. For example, theconstituent components of the polishing agent may be stored separatelyas a slurry comprising the abrasive grains and a fluid medium, anadditive solution containing the first additive and a fluid medium, andan additive solution containing the second additive, the third additiveand a fluid medium.

In the polishing agent set, the slurry and the additive solution aremixed immediately before polishing or during polishing to prepare thepolishing agent. A one-pack polishing agent may be stored as a polishingagent storage solution with a reduced fluid medium content, and used bydilution with a fluid medium during polishing. A multi-pack polishingagent set may be stored as a slurry storage solution and additivesolution storage solution with reduced fluid medium contents, and usedby dilution with a fluid medium during polishing.

In the case of a one-pack polishing agent, the method used to supply thepolishing agent onto the polishing platen may be a method for supplyingthe polishing agent by direct liquid conveyance; a method for conveyingthe polishing agent storage solution and the fluid medium throughseparate tubes, merging them together and then supplying; or a methodfor mixing the polishing agent storage solution and the fluid mediumbeforehand and then supplying.

For storage as a multi-pack polishing agent set separated into a slurryand an additive solution, the polishing rate can be adjusted byoptionally varying the composition of these liquids. When a polishingagent set is used for polishing, examples of the method for supplyingthe polishing agent onto the polishing platen includes the followingmethod. For example, there may be used a method for conveying the slurryand the additive solution through separate tubes and merging the tubesto mix and then supplying; a method for conveying the slurry storagesolution, the additive solution storage solution and a fluid mediumthrough separate tubes and merging the tubes to mix and then supplying;a method for mixing the slurry and the additive solution beforehand andthen supplying; or a method for mixing the slurry storage solution, theadditive solution storage solution and a fluid medium beforehand andthen supplying. There may also be used a method in which the slurry andthe additive solution of the polishing agent set are each supplied ontothe polishing platen. In this case, the polishing agent obtained bymixing the slurry and the additive solution on the polishing platen isused for polishing of the surface to be polished.

(Method for Polishing Base)

The method for polishing a base of the present embodiment may comprise apolishing step of polishing the surface to be polished of a base usingthe one-pack polishing agent, or it may comprise a polishing step ofpolishing the surface to be polished of a base using the polishing agentobtained by mixing at least the slurry and the additive solution of thepolishing agent set. The method for polishing a base of the presentembodiment may be a method for polishing a base having an insulatingmaterial and a stopper material, and for example, it may comprise apolishing step of selectively polishing the insulating material withrespect to the stopper material using the one-pack polishing agent, orthe polishing agent obtained by mixing the slurry and the additivesolution of the polishing agent set. In this case, the base may have amember containing the insulating material and a member containing thestopper material (stopper), for example. The stopper material ispreferably polysilicon and silicon nitride, and more preferablypolysilicon. The phrase “selectively polish material A with respect tomaterial B” means that the polishing rate for material A is higher thanthe polishing rate for material B under the same polishing conditions.It means, for example, that the material A is polished with thepolishing rate ratio of the polishing rate for material A with respectto the polishing rate for material B being 150 or more.

In the polishing step, for example, under the condition that thematerial to be polished of the base which has the material to bepolished is pressed against the polishing pad of a polishing platen, thepolishing agent is supplied between the material to be polished and thepolishing pad, and the base and the polishing platen are moved relativeto each other to polish the surface to be polished of the material to bepolished. For example, at least a portion of the material to be polishedis removed by the polishing in the polishing step.

Examples of the base which is to be polished include a substrate, andfor example, it may be a substrate comprising a material to be polishedformed on a substrate for semiconductor element production (for example,a semiconductor substrate in which an STI pattern, gate pattern orwiring pattern has been formed). Examples of the material to be polishedinclude an insulating material such as silicon oxide; and a stoppermaterial such as polysilicon or silicon nitride. The material to bepolished may be a single material or a plurality of materials. When aplurality of materials are exposed on the surface to be polished, theymay be considered as the material to be polished. The material to bepolished may be in the form of a film (film to be polished), such as asilicon oxide film, a polysilicon film and a silicon nitride film.

By polishing a material to be polished (for example, an insulatingmaterial such as silicon oxide) formed on such substrate with thepolishing agent and removing the unwanted sections, it is possible toeliminate irregularities on the surface of the material to be polished,to produce a smooth surface over the entire surface of the material tobe polished. The polishing agent of the present embodiment is preferablyused for polishing of a surface to be polished containing silicon oxide.

In the present embodiment, it is possible to polish an insulatingmaterial in a base having an insulating material containing siliconoxide on at least the surface, a stopper (polishing stop layer) disposedas the lower layer of the insulating material, and a semiconductorsubstrate disposed under the stopper. The stopper material composing thestopper is a material with a lower polishing rate than the insulatingmaterial, and it is preferably polysilicon, silicon nitride or the like.With such a base, excessive polishing of the insulating material can beprevented by stopping the polishing when the stopper have exposed, andtherefore, it is possible to improve flatness of the surface of the baseafter polishing.

Examples of the forming method for a material to be polished include aCVD method such as a low-pressure CVD method, a sub-atmospheric pressureCVD method and a plasma CVD method; a spin coating method in which aliquid material is coated onto a substrate which is spinning.

Silicon oxide can be obtained using a low-pressure CVD method, forexample, by thermal reaction of monosilane (SiH₄) and oxygen (O₂).Silicon oxide is also obtained using a sub-atmospheric pressure CVDmethod, for example, by thermal reaction of tetraethoxysilane(Si(OC₂H₅)₄) and ozone (O₃). As other example, silicon oxide is likewiseobtained by plasma reaction of tetraethoxysilane and oxygen.

Silicon oxide can be obtained using a spin coating method, for example,by coating a liquid starting material containing inorganic polysilazane,inorganic siloxane or the like onto a substrate and conductingthermosetting reaction in a furnace body or the like.

Examples of the forming method for polysilicon include a low-pressureCVD method in which monosilane is subjected to thermal reaction, and aplasma CVD method in which monosilane is subjected to plasma reaction.

Examples of the forming method for silicon nitride include alow-pressure CVD method in which dichlorosilane and ammonia arethermally reacted, and a plasma CVD method in which monosilane, ammoniaand nitrogen are subjected to plasma reaction. The silicon nitrideobtained by such a method may contain elements other than silicon andnitrogen, such as carbon or hydrogen, in order to adjust the materialquality.

In order to stabilize the materials such as silicon oxide, polysiliconand silicon nitride which are obtained by such methods, heat treatmentmay be performed at a temperature of 200° C. to 1000° C. as necessary.The silicon oxide obtained by such methods may also contain smallamounts of boron (B), phosphorus (P), carbon (C) or the like in order toincrease the embedding property.

Hereinafter, the polishing method of the present embodiment will bedescribed using a polishing method for a semiconductor substrate onwhich an insulating material has been formed, as an example. In thepolishing method of the present embodiment, the polishing apparatus usedcan be a common polishing apparatus having a holder capable of holding abase, such as a semiconductor substrate, which has the surface to bepolished, and a polishing platen on which a polishing pad can bemounted. Rotational speed-variable motors or the like are mounted on theholder and the polishing platen, respectively. The polishing apparatusused can be the polishing apparatus: Reflexion manufactured by AppliedMaterials, Inc.

The polishing pad used can be a common nonwoven fabric, a foam body, anon-foam body or the like. Material for the polishing pad used can be aresin such as polyurethane, acryl, polyester, an acryl-ester copolymer,polytetrafluoroethylene, polypropylene, polyethylene,poly-4-methylpentene, cellulose, cellulose ester, polyamide (forexample, nylon (trademark) and aramid), polyimide, polyimideamide, apolysiloxane copolymer, an oxirane compound, a phenol resin,polystyrene, polycarbonate, or an epoxy resin. Particularly, materialfor the polishing pad is preferably foamed polyurethane and non-foamedpolyurethane, from the viewpoint of a polishing rate and flatness. Thepolishing pad may be furrowed to allow accumulation of the polishingagent.

The polishing conditions are not limited, but the rotational speed(number of rotations) of the polishing platen is preferably 200 min⁻¹ orless so that the semiconductor substrate does not fly out, and thepolishing pressure (machining load) on the semiconductor substrate ispreferably 100 kPa or less from the viewpoint of sufficientlysuppressing the generation of polishing scratches. The polishing agentis preferably continuously supplied to the polishing pad with a pump orthe like during polishing. The amount supplied is not limited, butpreferably the surface of the polishing pad is covered by the polishingagent at all times.

The semiconductor substrate after polishing is preferably sufficientlywashed in flowing water to remove the particles adhering to thesubstrate. The washing may be performed using dilute hydrofluoric acidor ammonia water in addition to purified water, and a brush may be usedto increase the washing efficiency. It is preferable that, afterwashing, the water droplets adhering to the semiconductor substrate areremoved off using a spin dryer or the like, and then the semiconductorsubstrate is dried.

The polishing agent, polishing agent set and polishing method of thepresent embodiment can be suitably used for formation of an STI. Forformation of an STI, the lower limit of the polishing rate ratio for theinsulating material (for example, silicon oxide) with respect to thestopper material (for example, polysilicon) is preferably 150 or more,more preferably 250 or more, further preferably 350 or more,particularly preferably 500 or more, and extremely preferably 700 ormore. If the polishing rate ratio is lower than 150, the magnitude ofthe polishing rate for insulating material with respect to the polishingrate for stopper material is small, and therefore, it will tend to bedifficult to halt polishing at the prescribed location during formationof the STI. If the polishing rate ratio is 150 or more, on the otherhand, it will be easier to halt polishing, which is more suitable forSTI formation.

The polishing agent, polishing agent set and polishing method of thepresent embodiment can also be used for polishing of pre-metalinsulating materials. Examples of the pre-metal insulating materialsinclude phosphorus-silicate glass and boron-phosphorus-silicate glass inaddition to silicon oxide, as well as silicon oxyfluoride andfluorinated amorphous carbon.

The polishing agent, polishing agent set and polishing method of thepresent embodiment can also be applied for materials other thaninsulating materials such as silicon oxide. Examples of such materialsinclude high permittivity materials such as Hf-based, Ti-based andTa-based oxides; semiconductor materials such as silicon, amorphoussilicon, SiC, SiGe, Ge, GaN, GaP, GaAs and organic semiconductors;phase-change materials such as GeSbTe; inorganic conductive materialssuch as ITO; and polymer resin materials such as polyimide-based,polybenzooxazole-based, acrylic, epoxy-based and phenol-based materials.

The polishing agent, polishing agent set and polishing method of thepresent embodiment can be applied not only for polishing of film-likematerials, but also for various types of substrates made of glass,silicon, SiC, SiGe, Ge, GaN, GaP, GaAs, sapphire, plastics or the like.

The polishing agent, polishing agent set and polishing method of thepresent embodiment can be used not only for production of semiconductorelements, but also for production of image display devices such as TETsand organic ELs; optical parts such as photomasks, lenses, prisms,optical fibers and single crystal scintillators; optical elements suchas optical switching elements and optical waveguides; light-emittingelements such as solid lasers and blue laser LEDs; and magnetic storagedevices such as magnetic disks and magnetic heads.

EXAMPLES

Hereinafter, the present invention will be specifically described withreference to Examples, with the understanding that the invention is notlimited thereto.

<Synthesis of Hydroxide of Tetravalent Metal Element>

After 4.968 L of water was charged in a container, 0.143 L of a ceriumammonium nitrate aqueous solution having a concentration of 50 mass %(general formula Ce(NH₄)₂(NO₃)₆, formula weight 548.2 g/mol,manufactured by NIHON KAGAKU SANGYO CO., LTD., product name 50% CANliquid) was added and mixed. Then, the liquid temperature was adjustedto 40° C. to obtain a metal salt aqueous solution (metal saltconcentration: 0.037 mol/L).

Next, imidazole was dissolved in water to prepare 0.912 L of an aqueoussolution having a concentration of 0.7 mol/L. Then, the liquidtemperature was adjusted to a temperature of 40° C. to obtain an alkaliliquid.

The container containing the above-described metal salt aqueous solutiontherein was placed in a water tank filled with water. The watertemperature of the water tank was adjusted to 40° C. using anexternal-circulating device Coolnics Circulator (manufactured by TokyoRikakikai Co., Ltd. (EYELA), product name Cooling Thermopump CTP101).The above-described alkali liquid was added into the container at amixing rate of 1.7×10⁻⁶ m³/min while maintaining the water temperatureat 40° C. and stirring the metal salt aqueous solution at a stirringrate of 400 min⁻¹, to obtain a slurry precursor 1 comprising abrasivegrains including a hydroxide of tetravalent cerium. The metal saltaqueous solution was stirred using a 3-bladed pitched paddle having atotal blade length of 5 cm.

The obtained slurry precursor 1 was subjected to ultrafiltration whilebeing circulated, using a hollow fiber filter having a cutoff molecularweight of 50000 to remove ion components until the conductivity became50 mS/m or less, and therefore, a slurry precursor 2 was obtained. Theabove-described ultrafiltration was performed while adding water so asto maintain a constant water level of a tank containing the slurryprecursor 1, using a fluid level sensor. The content of non-volatilecomponent (the content of the abrasive grains including a hydroxide oftetravalent cerium) of the slurry precursor 2 was calculated by taking aproper amount of the obtained slurry precursor 2 and measuring the massbefore and after drying. If the content of the non-volatile componentwas less than 1.0 mass % at this stage, ultrafiltration was furtherperformed such that it was concentrated to about more than 1.1 mass %.Finally, a proper amount of water was added to prepare a ceriumhydroxide slurry storage solution (particle content: 1.0 mass %).

<Structural Analysis of Abrasive Grains>

A suitable amount of the cerium hydroxide slurry storage solution wastaken and vacuum dried to isolate the abrasive grains, and then, washingwas sufficiently performed with purified water to obtain a sample. Theobtained sample was measured by FT-IR ATR method, and a peak for nitrateion (NO₃ ⁻) was observed in addition to a peak for hydroxide ion (OH⁻).The same sample was measured by XPS for nitrogen (N-XPS), and a peak fornitrate ion was observed while no peak for NH⁴⁺ was observed. Theseresults confirmed that the abrasive grains comprised in the ceriumhydroxide slurry storage solution at least partially contain particlesthought to have a nitrate ion bonded to a cerium element.

<Measurement of Absorbance and Light Transmittance>

A suitable amount of the cerium hydroxide slurry storage solution wastaken and diluted with water so that an abrasive grain content wasadjusted to 0.0065 mass % (65 ppm), to obtain a measuring sample(aqueous dispersion). Approximately 4 mL of this measuring sample wasplaced in a 1 cm-square cell, and the cell was set in aspectrophotometer (apparatus name: U3310) manufactured by Hitachi, Ltd.Spectrophotometry was performed in a wavelength range of 200 to 600 nmto measure the absorbance for light having a wavelength of 290 nm andthe absorbance for light having a wavelength of 450 to 600 nm. Theabsorbance for light having a wavelength of 290 nm was 1.207, and theabsorbance for light having a wavelength of 450 to 600 nm was less than0.010.

Approximately 4 mL of the cerium hydroxide slurry storage solution(particle content: 1.0 mass %) was placed in a 1 cm-square cell, and thecell was set in a spectrophotometer (apparatus name: U3310) manufacturedby Hitachi, Ltd. Spectrophotometry was performed in a wavelength rangeof 200 to 600 nm to measure the absorbance for light having a wavelengthof 400 nm and the light transmittance for light having a wavelength of500 nm. The absorbance for light having a wavelength of 400 nm was 2.25,and the light transmittance for light having a wavelength of 500 nm was99%/cm.

<Measurement of Content of Non-Volatile Component in Liquid Phase>

A centrifuge tube (tube) included in an ultracentrifuge (device name:70P-72) manufactured by Hitachi Koki Co., Ltd., was filled with thecerium hydroxide slurry storage solution (particle content: 1.0 mass %),and the ultracentrifuge was used for 50 minutes of centrifugation at arotational speed of 50000 min⁻¹. A precipitate was confirmed in thebottom of the centrifuge tube. In the ultracentrifuge, the tube anglewas 26°; the minimum radius R_(min) was 3.53 cm; the maximum radiusR_(max) was 7.83 cm; and the average radius R_(av) was 5.68 cm. Thecentrifugal acceleration calculated from average radius R_(av) was158756 G=1.59×10⁵ G, 5.0 g of the liquid phase was sampled from thecentrifuge tube after centrifugal separation, and placed in an aluminumdish, and dried at 150° C. for 1 hour. The content of non-volatilecomponent (the content of the cerium hydroxide particles) contained inthe liquid phase was calculated by measuring the mass before and afterdrying. The content of non-volatile component was 812 ppm.

Preparation of CMP Polishing Agent Example 1

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, 0.001 mass % ofpolyallylamin, and 0.001 mass % (10 ppm) of sulfanilic acid was preparedby mixing 100 g of an additive solution storage solution containing 5mass % of polyethylene glycol [PEG #400 manufactured by Lion Corp.,weight-average molecular weight: 400] and 95 mass % of water, 50 g of acerium hydroxide slurry storage solution, 830 g of water, 10 g of anaqueous solution containing 0.1 mass % of polyallylamine [PAA-01manufactured by Nittobo Medical Co., Ltd., weight-average molecularweight: 1.6×10³] as a cationic polymer, and 10 g of an aqueous solutioncontaining 0.1 mass % of sulfanilic acid as an amino group-containingsulfonic acid compound. The pH of the CMP polishing agent was adequatelyadjusted to 6.1 using imidazole.

Example 2

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, 0.001 mass % ofpolyallylamine, and 0.005 mass % (50 ppm) of sulfanilic acid wasprepared in the same manner as Example 1, except for the sulfanilic acidcontent. The pH of the CMP polishing agent was adequately adjusted to6.2 using imidazole.

Example 3

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, 0.001 mass % ofpolyallylamine, and 0.01 mass % (100 ppm) of sulfanilic acid wasprepared in the same manner as Example 1, except for the sulfanilic acidcontent. The pH of the CMP polishing agent was adequately adjusted to6.4 using imidazole.

Example 4

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, 0.003 mass % of adiallyldimethylammonium chloride/acrylamide copolymer, and 0.005 mass %(50 ppm) of sulfanilic acid was prepared by mixing 100 g of an additivesolution storage solution containing 5 mass % of polyethylene glycol[PEG #44000 manufactured by Lion Corp., weight-average molecular weight:4.0×10³] and 95 mass % of water, 50 g of a cerium hydroxide slurrystorage solution, 770 g of water, 30 g of an aqueous solution containing0.1 mass % of a diallyldimethylammonium chloride/acrylamide copolymer[PAS-J-81 manufactured by Nittobo Medical Co., Ltd., weight-averagemolecular weight: 200×10³] as a cationic polymer, and 50 g of an aqueoussolution containing 0.1 mass % of sulfanilic acid as an aminogroup-containing sulfonic acid compound. The pH of the CMP polishingagent was adequately adjusted to 6.0 using imidazole.

Example 5

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, 0.003 mass % of adiallyldimethylammonium chloride/acrylamide copolymer, and 0.005 mass %(50 ppm) of sulfanilic acid was prepared by mixing 100 g of an additivesolution storage solution containing 5 mass % of polyethylene glycol[PEG #600 manufactured by Lion Corp., weight-average molecular weight:600] and 95 mass % of water, 50 g of a cerium hydroxide slurry storagesolution, 770 g of water, 30 g of an aqueous solution containing 0.1mass % of a diallyldimethylammonium chloride/acrylamide copolymer[PAS-J-81 manufactured by Nittobo Medical Co., Ltd., weight-averagemolecular weight: 200×10³] as a cationic polymer, and 50 g of an aqueoussolution containing 0.1 mass % of sulfanilic acid as an aminogroup-containing sulfonic acid compound. The pH of the CMP polishingagent was adequately adjusted to 6.0 using imidazole.

Example 6

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, 0.003 mass % ofpolyethyleneimine [EPOMIN P-1000 manufactured by Nippon Shokubai Co.,Ltd., weight-average molecular weight: 70×10³], and 0.005 mass % (50ppm) of sulfanilic acid was prepared in the same manner as Example 5,except for the type of the cationic polymer. The pH of the CMP polishingagent was adequately adjusted to 6.0 using imidazole.

Example 7

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, 0.003 mass % of adiallyldimethylammonium chloride/acrylamide copolymer [PAS-J-81manufactured by Nittobo Medical Co., Ltd., weight-average molecularweight: 200×10³], and 0.005 mass % (50 ppm) of 2-aminoethanesulfonicacid was prepared in the same manner as Example 5, except for the typeof the amino group-containing sulfonic acid compound. The pH of the CMPpolishing agent was adequately adjusted to 6.1 using imidazole.

Example 8

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyglycerin, 0.003 mass % of adiallyldimethylammonium chloride/acrylamide copolymer, and 0.005 mass %(50 ppm) of sulfanilic acid was prepared by mixing 100 g of an additivesolution storage solution containing 5 mass % of a polyglycerin decamer(PGL decamer) [PGL750 manufacture by Sakamoto Yakuhin Kogyo Co., Ltd.,weight-average molecular weight: 750] and 95 mass % of water, 50 g of acerium hydroxide slurry storage solution, 770 g of water, 30 g of anaqueous solution containing 0.1 mass % of a diallyldimethylammoniumchloride/acrylamide copolymer [PAS-J-81 manufactured by Nittobo MedicalCo., Ltd., weight-average molecular weight: 200×10³] as a cationicpolymer, and 50 g of an aqueous solution containing 0.1 mass % ofsulfanilic acid as an amino group-containing sulfonic acid compound. ThepH of the CMP polishing agent was adequately adjusted to 6.0 usingimidazole.

Example 9

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of a vinyl alcohol polymer, 0.003 mass % of adiallyldimethylammonium chloride/acrylamide copolymer, and 0.005 mass %(50 ppm) of sulfanilic acid was prepared by mixing 100 g of an additivesolution storage solution containing 5 mass % of a vinyl alcohol polymer[PVA-403 by Kuraray Co., Ltd., mean polymerization degree: 300,saponification degree: 80 mol %, weight-average molecular weight:14×10³] and 95 mass % of water, 50 g of a cerium hydroxide slurrystorage solution, 770 g of water, 30 g of an aqueous solution containing0.1 mass % of a diallyldimethylammonium chloride/acrylamide copolymer[PAS-J-81 manufactured by Nittobo Medical Co., Ltd., weight-averagemolecular weight: 200×10³] as a cationic polymer, and 50 g of an aqueoussolution containing 0.1 mass % of sulfanilic acid as an aminogroup-containing sulfonic acid compound. The pH of the CMP polishingagent was adequately adjusted to 6.3 using imidazole.

Example 10

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyoxyethylene styrenated phenyl ether, 0.003mass % of a diallyldimethylammonium chloride/acrylamide copolymer, and0.005 mass % (50 ppm) of sulfanilic acid was prepared by mixing 100 g ofan additive solution storage solution containing 5 mass % ofpolyoxyethylene styrenated phenyl ether [NOIGEN EA-137 manufactured byDai-Ichi Kogyo Seiyaku Co., Ltd., weight-average molecular weight: 700]and 95 mass % of water, 50 g of a cerium hydroxide slurry storagesolution, 770 g of water, 30 g of an aqueous solution containing 0.1mass % of a diallyldimethylammonium chloride/acrylamide copolymer[PAS-J-81 manufactured by Nittobo Medical Co., Ltd., weight-averagemolecular weight: 200×10³] as a cationic polymer, and 50 g of an aqueoussolution containing 0.1 mass % of sulfanilic acid as an aminogroup-containing sulfonic acid compound. The pH of the CMP polishingagent was adequately adjusted to 6.1 using imidazole.

Example 11

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyoxyethylene styrenated phenyl ether, 0.003mass % of a diallyldimethylammonium chloride/acrylamide copolymer, and0.01 mass % (100 ppm) of 2,4-diaminobenzensulfonic acid was prepared bymixing 100 g of an additive solution storage solution containing 5 mass% of polyoxyethylene styrenated phenyl ether [NOIGEN EA-207Dmanufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd., weight-averagemolecular weight: 4500] and 95 mass % of water, 50 g of a ceriumhydroxide slurry storage solution, 720 g of water, 30 g of an aqueoussolution containing 0.1 mass % of a diallyldimethylammoniumchloride/acrylamide copolymer [PAS-J-81 manufactured by Nittobo MedicalCo., Ltd., weight-average molecular weight: 200×10³] as a cationicpolymer, and 100 g of an aqueous solution containing 0.1 mass % of2,4-diaminobenzensulfonic acid as an amino group-containing sulfonicacid compound. The pH of the CMP polishing agent was adequately adjustedto 6.1 using imidazole.

Example 12

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polypropylene glycol, 0.003 mass % of adiallyldimethylammonium chloride/acrylamide copolymer, and 0.003 mass %(30 ppm) of sulfanilic acid was prepared by mixing 100 g of an additivesolution storage solution containing 5 mass % of polypropylene glycol[UNIOR D-700 manufactured by NOF Corporation, weight-average molecularweight: 700] and 95 mass % of water, 50 g of a cerium hydroxide slurrystorage solution, 790 g of water, 30 g of an aqueous solution containing0.1 mass % of a diallyldimethylammonium chloride/acrylamide copolymer[PAS-J-81 manufactured by Nittobo Medical Co., Ltd., weight-averagemolecular weight: 200×10³] as a cationic polymer, and 30 g of an aqueoussolution containing 0.1 mass % of sulfanilic acid as an aminogroup-containing sulfonic acid compound. The pH of the CMP polishingagent was adequately adjusted to 6.0 using imidazole.

Comparative Example 1

A CMP polishing agent with a pH of 5.9 containing 0.05 mass % of ceriumhydroxide particles was prepared by mixing 50 g of a cerium hydroxideslurry storage solution, 940 g of water, and 10 g of an aqueous solutionof 1 mass % imidazole.

Comparative Example 2

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles and 0.001 mass % of polyallylamine was prepared by mixing 50 gof a cerium hydroxide slurry storage solution, 940 g of water, and 10 gof an aqueous solution of 0.1 mass % of polyallylamine [PAA-01manufactured by Nittobo Medical Co., Ltd., weight-average molecularweight: 1.6×10³]. The pH of the CMP polishing agent was adequatelyadjusted to 6.0 using imidazole.

Comparative Example 3

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles and 0.5 mass % of polyethylene glycol was prepared by mixing100 g of an additive solution storage solution containing 5 mass % ofpolyethylene glycol [PEG #600 manufactured by Lion Corp., weight-averagemolecular weight: 600] and 95 mass % of water, 50 g of a ceriumhydroxide slurry storage solution, and 850 g of water. The pH of the CMPpolishing agent was adequately adjusted to 6.2 using imidazole.

Comparative Example 4

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles and 0.5 mass % of a vinyl alcohol polymer was prepared bymixing 100 g of an additive solution storage solution containing 5 mass% of a vinyl alcohol polymer [PVA-403 manufactured by Kuraray Co., Ltd.,mean polymerization degree: 300, saponification degree: 80 mol %,weight-average molecular weight: 14×10³] and 95 mass % of water, 50 g ofa cerium hydroxide slurry storage solution, and 850 g of water. The pHof the CMP polishing agent was adequately adjusted to 5.8 usingimidazole.

Comparative Example 5

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of a vinyl alcohol polymer, and 0.0001 mass % ofpolyallylamine was prepared in the same manner as Comparative Example 4,except that polyallylamine [PAA-01 manufactured by Nittobo Medical Co.,Ltd., weight-average molecular weight: 1.6×10³] was added as a cationicpolymer. The pH of the CMP polishing agent was adequately adjusted to5.9 using imidazole.

Comparative Example 6

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 1 mass % of a vinyl alcohol polymer, and 0.0008 mass % ofpolyallylamine was prepared by mixing 100 g of an additive solutionstorage solution containing 10 mass % of a vinyl alcohol polymer[PVA-403 by Kuraray Co., Ltd., mean polymerization degree: 300,saponification degree: 80 mol %, weight-average molecular weight:14×10³], 0.008 mass % of polyallylamine [PAA-08 by Nittobo Medical Co.,Ltd., weight-average molecular weight: 8.0×10³], and 89.992 mass % ofwater, 50 g of a cerium hydroxide slurry storage solution, and 850 g ofwater. The pH of the CMP polishing agent was adequately adjusted to 6.0using imidazole.

Comparative Example 7

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.007 mass % of polyethylene glycol, and 0.015 mass % ofchitosan was prepared by mixing 100 g of an additive solution storagesolution containing 0.07 mass % of polyethylene glycol [PEG #600manufactured by Lion Corp., weight-average molecular weight: 600], 0.15mass % of chitosan [DAICHITOSAN 100D manufactured by Dainichiseika Color& Chemicals Mfg. Co., Ltd., deacetylation degree: ≥98%], and 99.78 mass% of water, 50 g of a cerium hydroxide slurry storage solution, and 850g of water. The pH of the CMP polishing agent was adequately adjusted to6.4 using imidazole.

Comparative Example 8

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of a vinyl alcohol polymer, and 0.001 mass % of aN,N-dimethylaminopropylacrylamide polymer was prepared by mixing 100 gof an additive solution storage solution containing 5 mass % of a vinylalcohol polymer [PVA-403 manufactured by Kuraray Co., Ltd., meanpolymerization degree: 300, saponification degree: 80 mol %,weight-average molecular weight: 14×10³], 0.01 mass % of aN,N-dimethylaminopropylacrylamide polymer [weight-average molecularweight: 23×10³], and 94.99 mass % of water, 50 g of a cerium hydroxideslurry storage solution, and 850 g of water. The pH of the CMP polishingagent was adequately adjusted to 6.1 using imidazole.

The N,N-dimethylaminopropylacrylamide polymer was prepared by thefollowing procedure. First, 15 g of N,N-dimethylaminopropylacrylamide(DMAPAA manufactured by Kohjin Co., Ltd.) and 281 g of water were placedin a round bottom flask and nitrogen gas was introduced in. An aqueoussolution composed of 696 mg of2,2′-azobis(2-methylpropionamidine)dihydrochloride and 4 g of water wasadded while heating at 80° C. and stirring. After heating and stirringat 80° C. for 2 hours, it was cooled to room temperature (25° C.) toobtain a N,N-dimethylaminopropylacrylamide polymer with a concentrationof 5 mass %.

Comparative Example 9

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles and 0.005 mass % (50 ppm) of sulfanilic acid was prepared bymixing 50 g of a cerium hydroxide slurry storage solution, 900 g ofwater, and 50 g of an aqueous solution containing 0.1 mass % ofsulfanilic acid as an amino group-containing sulfonic acid compound. ThepH of the CMP polishing agent was adequately adjusted to 6.1 usingimidazole.

Comparative Example 10

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.5 mass % of polyethylene glycol, and 0.005 mass % (50 ppm)of sulfanilic acid was prepared by mixing 100 g of an additive solutionstorage solution containing 5 mass % of polyethylene glycol [PEG #600manufactured by Lion Corp., weight-average molecular weight: 600] and 95mass % of water, 50 g of a cerium hydroxide slurry storage solution, 800g of water, and 50 g of an aqueous solution containing 0.1 mass % ofsulfanilic acid as an amino group-containing sulfonic acid compound. ThepH of the CMP polishing agent was adequately adjusted to 6.1 usingimidazole.

Comparative Example 11

A CMP polishing agent comprising 0.05 mass % of cerium hydroxideparticles, 0.001 mass % of polyallylamine, and 0.005 mass % (50 ppm) ofsulfanilic acid was prepared by mixing 50 g of a cerium hydroxide slurrystorage solution, 890 g of water, 10 g of an aqueous solution containing0.1 mass % of polyallylamine [PAA-01 manufactured by Nittobo MedicalCo., Ltd., weight-average molecular weight: 1.6×10³] as a cationicpolymer, and 50 g of an aqueous solution containing 0.1 mass % ofsulfanilic acid as an amino group-containing sulfonic acid compound. ThepH of the CMP polishing agent was adequately adjusted to 6.2 usingimidazole.

<Evaluation of Liquid Properties>

The pH of the CMP polishing agent and the average particle diameter ofthe cerium hydroxide particles in the cerium hydroxide slurry storagesolution were evaluated under the following conditions.

(pH)

Measuring temperature: 25±5° C.

Measuring apparatus: Model PHL-40 manufactured by DKK Corp.

Measuring method: After 2-point calibration using a standard buffersolution (phthalate pH buffer solution: pH: 4.01 (25° C.), neutralphosphate pH buffer solution: pH 6.86 (25° C.)), the electrode wasplaced in the CMP polishing agent, and then the pH was measured with themeasuring apparatus described above after at least 2 min passed forstabilization.

(Average Particle Diameter of Cerium Hydroxide Particles)

The average particle diameter of the cerium hydroxide particles in thecerium hydroxide slurry storage solution was measured using N5 (tradename) manufactured by Beckman Coulter, Inc. The measuring method was asfollows. First, an aqueous dispersion having an abrasive grain contentadjusted to 0.2 mass % was prepared, and approximately 1 mL of theaqueous dispersion was placed in a 1 cm-square cell and the cell was setin the N5. Measurement was performed at 25° C. with the refractive indexof the dispersion medium set to 1.333 and the viscosity of thedispersion medium set to 0.887 mPa·s, and the value indicated asUnimodal Size Mean was read off. As a result, the average particlediameter of the abrasive grains was 24 nm.

<CMP Evaluation>

The CMP polishing agent was used for polishing of substrates to bepolished, under the following polishing conditions. For ComparativeExamples 1, 2, 9, and 11, the pattern wafer was not polished since thepolishing rate ratio between a silicon oxide film and a polysilicon filmwas 10 or less, as a result of primary screening in non-pattern wafers.

(CMP Polishing Conditions)

-   -   Polishing apparatus: Reflexion (Applied Materials, Inc.)    -   CMP polishing agent flow rate: 200 mL/min    -   Substrates to be polished:        (Non-Pattern Wafers)

As blanket wafers without formation of a pattern, there were used asubstrate having a 1 μm-thick silicon oxide film formed on a siliconsubstrate by plasma CVD method, and a substrate having a 0.2 μm-thickpolysilicon film formed on a silicon substrate by CVD method.

(Pattern Wafers)

As a pattern wafer with a test pattern formed thereon, there was used awafer (trade name: 764 wafer, diameter: 300 mm) manufactured bySematech. The pattern wafer was a wafer obtained through the followingsteps:

(1) laminating a polysilicon film as a stopper on a silicon substrate;

(2) forming a trench; and

(3) laminating a silicon oxide film (SiO₂ film) as an insulatingmaterial on the silicon substrate and polysilicon film so as to fill inthe polysilicon film and the trench.

The silicon oxide film was formed by an HDP (High Density Plasma)method.

-   -   Polishing pad: Foamed polyurethane resin with closed cells        (Model No. IC1010 manufactured by Rohm & Haas, Japan), Shore D        hardness: 60    -   Polishing pressure: 16.5 kPa (2.4 psi)    -   Relative speed between substrate and polishing platen: 85 m/min    -   Polishing time: The blanket wafer was polished for 1 min. The        pattern wafer was polished until the polysilicon stopper film as        the stopper was exposed. The degree of progression of dishing        was confirmed by further shaving for a time equal to the        polishing time until the polysilicon film was exposed.    -   Washing: CMP treatment was followed by washing with ultrasonic        water and drying with a spin dryer.

The pattern wafer used was one having sections with line (convex part) &space (concave part) widths of a 200 μm pitch and with a convex partpattern density of 50%. The line & space is a test pattern, and it is apattern comprising active sections masked by the polysilicon film as theconvex parts and trench sections with grooves as the concave parts,alternately arranged. “200 μm pitch for line & space and a convex partpattern density of 50%” means a pattern with alternating arrangement ofconvex part width: 100 μm and concave part width: 100 μm.

In the pattern wafer, the thickness of the silicon oxide film was 600 nmon both the silicon substrate at the concave parts and the polysiliconfilm at the convex parts. Specifically, as shown in FIG. 2, thethickness of the polysilicon film 2 on the silicon substrate 1 was 150nm, the thickness of the convex parts of the silicon oxide film 3 was600 nm, the thickness of the concave parts of the silicon oxide film 3was 600 nm, and the depth of the concave parts of the silicon oxide film3 was 500 nm (trench depth: 350 nm+polysilicon film thickness: 150 nm).

For evaluation of polishing of the pattern wafer, the wafer used was onehaving a remaining step height of 100 nm or less, obtained by polishingthe wafer above using a known CMP polishing agent with a self-stoppingproperty (property in which polishing rate is lowered when the remainingstep height of the test pattern is small). Specifically, the wafer usedwas one obtained by polishing using the polishing agent comprisingHS-8005-D4 manufactured by Hitachi Chemical Co., Ltd., HS-7303GPmanufactured by Hitachi Chemical Co., Ltd. and water in a proportion of2:1.2:6.8 until the thickness of the silicon oxide film reached 130 nmat the convex parts of a 1000 μm pitch and 50% density pattern.

<Evaluation of Polished Products>

[Polishing Rate for Blanket Wafer]

The polishing rates for films to be polished (silicon oxide film andpolysilicon film) which had been polished and washed under theconditions described above (polishing rate for silicon oxide: SiO₂RR,polishing rate for polysilicon: p-SiRR) were determined by the followingformula. The polishing rate ratio of the SiO₂RR with respect to thep-SiRR was calculated. The difference in film thickness of the film tobe polished before and after polishing was determined using alight-interference film thickness meter (trade name: F80 manufactured byFilmetrics Japan, Inc.).(Polishing rate: RR)=(Film thickness difference of film to be polishedbefore and after polishing (nm))/(polishing time (min))

[Evaluation of Pattern Wafer]

The residual film thickness of the polysilicon film at the convex partsof the pattern wafer which had been polished and washed under theconditions described above and the residual film thickness of thesilicon oxide film at the concave parts were measured and the remainingstep height (dishing) was determined by the following formula. A dishingprogression rate (nm/min) was calculated based on the polishing time(min). The film thickness of the film to be polished before and afterpolishing was determined using a light-interference film thickness meter(trade name: Nanospec AFT-5100 manufactured by Nanometrics, Inc.).Remaining step height (dishing) (350 nm+thickness of polysilicon film(nm)−(residual film thickness of silicon oxide film at concave parts(nm))

[Evaluation of Polishing Scratches]

A substrate to be polished (blanket wafer substrate having a siliconoxide film) which had been polished and washed under the conditionsdescribed above was dipped for 15 seconds in an aqueous solution of 0.5mass % hydrogen fluoride and washed with water for 60 seconds. Next, thesurface of the substrate to be polished was washed for 1 min using apolyvinyl alcohol brush while supplying water, and was dried. Complusmanufactured by Applied Materials, Inc. was used to detect defects of0.2 μm or more on the surface of the substrate to be polished.Furthermore, upon observation of the surface of the substrate to bepolished using the defect detection coordinates obtained by the Complusmanufactured by Applied Materials, Inc., and using an SEM Visionmanufactured by Applied Materials, Inc., the number of extractedpolishing scratches of 0.2 μm or more at the surface of the substrate tobe polished was counted. The number of polishing scratches was about 0to 3 (per wafer) in both Examples and Comparative Examples, indicatingthat generation of polishing scratches was sufficiently suppressed.

The measurement results obtained in Examples 1 to 12 and ComparativeExamples 1 to 11 are shown in Tables 1 to 4.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Abrasive Kind Hydroxide of Hydroxide of Hydroxide of Hydroxide ofHydroxide of Hydroxide of grains cerium cerium cerium cerium ceriumcerium Content (mass %) 0.05 0.05 0.05 0.05 0.05 0.05 Composition Firstadditive PEG#400 PEG#400 PEG#400 PEG#4000 PEG#600 PEG#600 Content (mass%) 0.5 0.5 0.5 0.5 0.5 0.5 Second additive PAA-01 PAA-01 PAA-01 PAS-J-81PAS-J-81 EPOMIN P-1000 Content (mass %) 0.001 0.001 0.001 0.003 0.0030.003 Third additive Sulfanilic Sulfanilic Sulfanilic SulfanilicSulfanilic Sulfanilic acid acid acid acid acid acid Content (mass %)0.001 0.005 0.01 0.005 0.005 0.005 pH 6.1 6.2 6.4 6.0 6.0 6.0 PolishingSiO₂RR (nm/min) 295 298 293 323 361 430 rate p-SiRR (nm/min) 0.2 0.3 0.20.2 0.2 0.2 Polishing rate 1475 993 1465 1615 1805 2150 ratio FlatnessDishing 8 4 2 3 4 3 progression rate (nm/min) Polishing scratches (perwafer) 0 0 1 0 0 2

TABLE 2 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12Abrasive Kind Hydroxide of Hydroxide of Hydroxide of Hydroxide ofHydroxide of Hydroxide of grains cerium cerium cerium cerium ceriumcerium Content (mass %) 0.05 0.05 0.05 0.05 0.05 0.05 Composition Firstadditive PEG#600 PGL decamer PVA-403 NOIGEN NOIGEN UNIOR EA-137 EA-207DD-700 Content (mass %) 0.5 0.5 0.5 0.5 0.5 0.5 Second additive PAS-J-81PAS-J-81 PAS-J-81 PAS-J-81 PAS-J-81 PAS-J-81 Content (mass %) 0.0030.003 0.003 0.003 0.003 0.003 Third additive 2-aminoethane SulfanilicSulfanilic Sulfanilic 2,4-diamino Sulfanilic sulfonic acid acid acidacid benzene acid sulfonic acid Content (mass %) 0.005 0.005 0.005 0.0050.01 0.003 pH 6.1 6.0 6.3 6.1 6.1 6.0 Polishing SiO₂RR (nm/min) 302 320210 290 315 224 rate p-SiRR (nm/min) 0.3 0.1 0.3 0.2 0.4 0.2 Polishingrate 1007 3200 700 1450 788 1120 ratio Flatness Dishing 6 7 5 7 7 8progression rate (nm/min) Polishing scratches (per wafer) 1 0 1 0 1 0

TABLE 3 Comparative Comparative Comparative Comparative ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Abrasive Kind Hydroxide of Hydroxide of Hydroxide of Hydroxide ofHydroxide of Hydroxide of grains cerium cerium cerium cerium ceriumcerium Content (mass %) 0.05    0.05 0.05 0.05 0.05 0.05 CompositionFirst additive — — PEG#600 PVA-403 PVA-403 PVA-403 Content (mass %) — —0.5 0.5 0.5 1 Second additive — PAA-01 — — PAA-01 PAA-08 Content (mass%) —    0.001 — — 0.0001 0.0008 Third additive — — — — — — Content (mass%) — — — — — — pH 5.9   6.0 6.2 5.8 5.9 6.0 Polishing SiO₂RR (nm/min)163 48 94 180 192 182 rate p-SiRR (nm/min) 62 90 4 12 1 0.8 Polishingrate 3  1> 24 15 192 228 ratio Flatness Dishing — — 66 106 SiO₂ at 75progression rate convexities, (nm/min) unremovable Polishing scratches(per wafer) 0  2 3 1 0 0

TABLE 4 Comparative Comparative Comparative Comparative ComparativeExample 7 Example 8 Example 9 Example 10 Example 11 Abrasive KindHydroxide of Hydroxide of Hydroxide of Hydroxide of Hydroxide of grainscerium cerium cerium cerium cerium Content (mass %) 0.05 0.05 0.05 0.05   0.05 Composition First additive PEG#600 PVA-403 — PEG#600 — Content(mass %) 0.007 0.5 — 0.5 — Second additive DAICHITOSAN N,N-dimethyl — —PAA-01 100D aminopropyl acrylamide polymer Content (mass %) 0.015 0.001— —    0.001 Third additive — — Sulfanilic Sulfanilic Sulfanilic acidacid acid Content (mass %) — — 0.005 0.005    0.005 pH 6.4 6.1 6.1 6.1  6.2 Polishing SiO₂RR (nm/min) 376 170 182 96 49 rate p-SiRR (nm/min)13 6 60 5 82 Polishing rate 29 28 3 19  1> ratio Flatness Dishing 122118 — 55 — progression rate (nm/min) Polishing scratches (per wafer) 0 20 0  2

Hereinafter, the results shown in Tables 1 to 4 will be described indetail.

In all of Examples 1 to 12, SiO₂RR was 200 nm/min or more, p-SiRR was 1nm/min or less, and the polishing rate ratio was 150 or more, indicatinga practicable sufficiently high polishing rate and a high polishing rateratio. In the evaluation of pattern wafer, the dishing progression rateis 8 nm/min or less, and the obtained result was suppressed progressionof dishing.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide apolishing agent, a polishing agent set and a method for polishing abase, which can provide excellent polishing selectivity for insulatingmaterial with respect to stopper material and achieve a high degree offlattening of the surface of a base after polishing, in a CMP techniquefor polishing an insulating material (STI insulating material, pre-metalinsulating material, interlayer insulating material or the like) using astopper.

REFERENCE SIGNS LIST

1: silicon substrate, 2: polysilicon film, 3: silicon oxide film, AR:angle rotor, A1: rotation axis, A2: tube angle, R_(min): minimum radius,R_(max): maximum radius, R_(av): average radius

The invention claimed is:
 1. A polishing agent comprising: a fluidmedium; abrasive grains containing a hydroxide of a tetravalent metalelement; a first additive; a second additive; and a third additive,wherein: the first additive is at least one selected from the groupconsisting of a compound having a polyoxyalkylene chain and a vinylalcohol polymer; the second additive is a cationic polymer; and thethird additive is an amino group-containing sulfonic acid compound. 2.The polishing agent according to claim 1, wherein the second additive isat least one selected from the group consisting of an allylaminepolymer, a diallylamine polymer, a vinylamine polymer and anethyleneimine polymer.
 3. The polishing agent according to claim 1,wherein the third additive is at least one selected from the groupconsisting of sulfamic acid, an aliphatic aminosulfonic acid, anaromatic aminosulfonic acid and their salts.
 4. The polishing agentaccording to claim 1, wherein a content of the third additive is 0.0005mass % or more and 0.2 mass % or less based on a total mass of thepolishing agent.
 5. The polishing agent according to claim 1, whereinthe hydroxide of a tetravalent metal element contains an anion,excluding a hydroxide ion, bonded to the tetravalent metal element.
 6. Apolishing agent set comprising constituent components of the polishingagent according to claim 1 stored as separate liquids containing a firstliquid and a second liquid, wherein the first liquid contains theabrasive grains, and the second liquid contains at least one selectedfrom the group consisting of the first additive, the second additive andthe third additive.
 7. A method for polishing a base, comprising a stepof polishing a surface to be polished of a base using the polishingagent according to claim
 1. 8. A method for polishing a base, comprisinga step of polishing a surface to be polished of a base using a polishingagent obtained by mixing at least the first liquid and the second liquidof the polishing agent set according to claim
 6. 9. A method forpolishing a base having an insulating material and a stopper material,the method comprising a step of selectively polishing the insulatingmaterial with respect to the stopper material using the polishing agentaccording to claim
 1. 10. A method for polishing a base having aninsulating material and a stopper material, the method comprising a stepof selectively polishing the insulating material with respect to thestopper material using a polishing agent obtained by mixing the firstliquid and the second liquid of the polishing agent set according toclaim
 6. 11. The method for polishing a base according to claim 9,wherein the stopper material is polysilicon.
 12. The method forpolishing a base according to claim 10, wherein the stopper material ispolysilicon.
 13. The method for polishing a base according to claim 7,wherein the surface to be polished contains silicon oxide.
 14. Themethod for polishing a base according to claim 8, wherein the surface tobe polished contains silicon oxide.
 15. The method for polishing a baseaccording to claim 9, wherein the insulating material contains siliconoxide.
 16. The method for polishing a base according to claim 10,wherein the insulating material contains silicon oxide.
 17. Thepolishing agent according to claim 2, wherein the second additivecomprises one or more structural units derived from at least oneselected from the group consisting of acrylamide, dimethylacrylamide,diethylacrylamide, hydroxyethylacrylamide, acrylic acid, methylacrylate, methacrylic acid, maleic acid, and sulfur dioxide.